[llvm] [AMDGPU][GlobalISel] Add register bank legalization for G_AMDGPU_BUFFER_LOAD_BYTE_AND_SHORT (PR #167798)

[Syadus Sefat via llvm-commits]

mssefat wrote:

I have moved the tests I initially added to raw.buffer.load.ll into a new file [buffer-load-byte-short.ll], which now contains all the suggested uniform and divergent tests.

https://github.com/llvm/llvm-project/pull/167798