[llvm] [AMDGPU] Fix selection of s_load_b96 on GFX11 (PR #108029)

[Jay Foad via llvm-commits]

jayfoad wrote:

> LGTM. I assume global-isel doesn't have this problem?

I think GISel is OK because it is already calling `AMDGPUInstrInfo::isUniformMMO` from `AMDGPURegisterBankInfo::isScalarLoadLegal`.

https://github.com/llvm/llvm-project/pull/108029