[llvm] [AMDGPU] Add regbankselect rules for G_ADD/SUB and variants (PR #159860)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

Imo should not add all those files with mir tests. 
add.ll and sub.ll should cover everything from the patch (missing uniform v2s16 test). Just update existing mir tests. 
If you really need to add new mir test try adding to existing file,
or if you need to make new mir test file, make one for all the types, e.g `regbankselect-add.mir`

https://github.com/llvm/llvm-project/pull/159860