[XeGPU] `xegpu-to-vc-func` pass ignores constant offsets of `xegpu.update_nd_offset`

A constant offset is when you simply put a number as an offset value instead of an index value:
```mlir
// constant offset
%1 = xegpu.update_nd_offset %0, [2, 0] : !xegpu.tensor_desc<2x16xf16>

// regular offset
%c2 = arith.constant 2 : index
%1 = xegpu.update_nd_offset %0, [%c2, 0] : !xegpu.tensor_desc<2x16xf16>
```

The "constant" offsets are then only available via `op.getConstantOffsets()` and the regular via `op.getOffsets()`. The `xegpu-to-vc-func` pass [only accesses regular offsets](https://github.com/intel/mlir-extensions/blob/5a7bb80ede5fe4fa8d56ee0dd77c4e5c1327fe09/lib/Conversion/XeGPUToVC/XeGPUToVC.cpp#L266) and ignores constant ones. Changing [this line of code](https://github.com/intel/mlir-extensions/blob/5a7bb80ede5fe4fa8d56ee0dd77c4e5c1327fe09/lib/Conversion/XeGPUToVC/XeGPUToVC.cpp#L266) to `op.getConstantOffsets()` makes the "constant" offsets to work and the regular ones to be ignored. Is this intended behavior that one of the offsets type is ignored or is this a bug?

reproducer

```mlir
// RUN: %python_executable %imex_runner --requires=l0-runtime -i %s --pass-pipeline-file=%p/xegpu-to-func-vc.pp \
// RUN: --runner imex-cpu-runner -e main \
// RUN: --entry-point-result=void \
// RUN: --shared-libs=%irunner_utils,%mlir_runner_utils,%mlir_c_runner_utils,%levelzero_runtime

module attributes {gpu.container_module} {
gpu.module @index_offset attributes {spirv.target_env = #spirv.target_env<#spirv.vce, api=OpenCL, #spirv.resource_limits<>>} {
gpu.func @index_offset(%arg0: memref<4x16xf16>) kernel attributes {VectorComputeFunctionINTEL, known_block_size = array, known_grid_size = array, spirv.entry_point_abi = #spirv.entry_point_abi<>} {
%c2 = arith.constant 2 : index

%0 = xegpu.create_nd_tdesc %arg0[0, 0] : memref<4x16xf16> -> !xegpu.tensor_desc<2x16xf16>
%1 = xegpu.update_nd_offset %0, [%c2, 0] : !xegpu.tensor_desc<2x16xf16>
%val = arith.constant dense<25.0> : vector<2x16xf16>
xegpu.store_nd %val, %1 : vector<2x16xf16>, !xegpu.tensor_desc<2x16xf16>
gpu.return
}
}

gpu.module @const_offset attributes {spirv.target_env = #spirv.target_env<#spirv.vce, api=OpenCL, #spirv.resource_limits<>>} {
gpu.func @const_offset(%arg0: memref<4x16xf16>) kernel attributes {VectorComputeFunctionINTEL, known_block_size = array, known_grid_size = array, spirv.entry_point_abi = #spirv.entry_point_abi<>} {
%0 = xegpu.create_nd_tdesc %arg0[0, 0] : memref<4x16xf16> -> !xegpu.tensor_desc<2x16xf16>
%1 = xegpu.update_nd_offset %0, [2, 0] : !xegpu.tensor_desc<2x16xf16>
%val = arith.constant dense<25.0> : vector<2x16xf16>
xegpu.store_nd %val, %1 : vector<2x16xf16>, !xegpu.tensor_desc<2x16xf16>
gpu.return
}
}

func.func @main() {
%c1 = arith.constant 1 : index

%result = memref.alloc() : memref<4x16xf16>

%gpu_result_index = gpu.alloc host_shared () : memref<4x16xf16>
gpu.launch_func @index_offset::@index_offset blocks in (%c1, %c1, %c1) threads in (%c1, %c1, %c1) args(%gpu_result_index : memref<4x16xf16>)
memref.copy %gpu_result_index, %result : memref<4x16xf16> to memref<4x16xf16>
%cast1 = memref.cast %result : memref<4x16xf16> to memref<*xf16>
call @printMemrefF16(%cast1) : (memref<*xf16>) -> ()
// offset was successfully applied
// [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
// [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
// [25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25],
// [25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25]]

%gpu_result_const = gpu.alloc host_shared () : memref<4x16xf16>
gpu.launch_func @const_offset::@const_offset blocks in (%c1, %c1, %c1) threads in (%c1, %c1, %c1) args(%gpu_result_const : memref<4x16xf16>)
memref.copy %gpu_result_const, %result : memref<4x16xf16> to memref<4x16xf16>
%cast2 = memref.cast %result : memref<4x16xf16> to memref<*xf16>
call @printMemrefF16(%cast2) : (memref<*xf16>) -> ()
// offset was ignored:
// [[25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25],
// [25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25],
// [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
// [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]]

return
}
func.func private @printMemrefF16(memref<*xf16>)
}

```

p.s. [an example of how to use `xegpu.update_nd_offset` in mlir documentation](https://mlir.llvm.org/docs/Dialects/XeGPU/#xegpuupdate_nd_offset-xegpuupdatendoffsetop) uses "constant" offsets and as far as I understand [IMEX llvm patches](https://github.com/intel/mlir-extensions/tree/main/build_tools/patches) do not modify the structure of `update_nd_offset`, so I would expect them to work.