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

[Petar Avramovic via llvm-commits]

https://github.com/petar-avramovic approved this pull request.

Small nit for title since there is no G_AMDGPU_BUFFER_LOAD_BYTE_AND_SHORT, can write "buffer_load byte and short"

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