[llvm] [AMDGPU] Use fake16 load/store with +real-true16 and sram-ecc (PR #161256)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

>     2. We might need to turn off D16 for spills. For example, spillv16.ll still has scratch_load_d16_b16. With true16 we might need to spill/restore a hi16/lo16 within a vgpr32 seperately and it sounds like it would be a problem with eccram. I am not sure what is the best way to approach this. The straightforward way I can think of is to construct an vgpr32 from a vgpr16 first and spill/restore it. Maybe there are better way.

This patch does not address spilling, it is separate. Although I am also not sure what is a best way here. Maybe really force spilling of the whole 32-bit superreg but that likely will mess up with a liveness of the other half.

https://github.com/llvm/llvm-project/pull/161256