multiple gpu streams created when lowering gpu to gpux

See opt result of `test/Integration/Dialect/XeGPU/vector_insert_1.mlir`.

when `main()` calls `test()` and both functions access GPU shared memory, IMEX will geenerate code like

```
func test(...) -> memref<...> {
s1 = gpuStreamCreate(...)
ret = gpuMemAlloc(s1, ...)
gpuLaunchKernel(ret, ...)
gpuWait()
gpuStreamDestroy(s1)
return ret
}

func main() {
s2 = gpuStreamCreate(...)
v = test(...)
gpuMemFree(s2, v)
gpuStreamDestroy(s2)
}
```

Note that it creates 2 streams `s1` and `s2`. Also note that, the result of `test` is allocated from `s1`, which is already destroyed at the end of `test`. And we are using `s2` to free the memory of the result.

This happens to work in L0 and Sycl runtime, but I guess it is not actually legal in them to create memory in one stream and free it in another. This will cause an error in opencl runtime, BTW.