[memutil] Allow compilation with memories > Width

If memories are larger than Width bit Verilator fails to compile the design
with (example error message for Width == 128):

`%Error: prim_util_memload.sv:44:23: Extracting 256 bits from only
128 bit number`.

The expected behavior is to return `0` (false) in the DPI call for memories larger than Width, but still allow compilation.

We probably need a localparam "WidthMax" which is used in the part-select `mem[index] = val[WidthMax-1:0];`.

Start in prim_util_memload.sv at the reported part-select around line 44 and inspect the DPI memory-load path. Confirm that memories wider than Width compile successfully and that the DPI call returns false for them; use the issue's example error and expected behavior to verify completion.

Written by the indexing model from the issue text.