[AMDGPU] Switch AnnotateUniformValues to MemorySSA

This shall speedup compilation and also remove threshold
limitations used by memory dependency analysis.

It also seem to fix the bug in the coalescer_remat.ll
where an SMRD load was used in presence of a potentially
clobbering store.

Fixes: SWDEV-272132

Differential Revision: https://reviews.llvm.org/D101962