[llvm] [AMDGPU] Check MIR after SIMemoryLegalizer instead of final ISA (PR #90601)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

I am not a fan of the idea to convert all memory legalizer tests to mir. Maybe you can add some specific mir tests instead?

https://github.com/llvm/llvm-project/pull/90601