AMDGPU: Implement waterfall loop for MIMG instructions with 256-bit SRsrc

AMDGPU: Implement waterfall loop for MIMG instructions with 256-bit SRsrc

Summary:
  When the resource descriptor is of vgpr, we need a waterfall loop
to read into a sgpr. In this patchm we generalized the  implementation
to work for any regster class sizes, and extend the work to MIMG
instructions.

Fixes: SWDEV-223405

Reviewers:
  arsenm, nhaehnle

Differential Revision:
  https://reviews.llvm.org/D82603