[AMDGPU] gfx11 FLAT Instructions

MachineCode Support for FLAT type instructions

Contributors:
Sebastian Neubauer <sebastian.neubauer@amd.com>

Patch 12/N for upstreaming of AMDGPU gfx11 architecture.

Depends on D125989

Reviewed By: rampitec, #amdgpu

Differential Revision: https://reviews.llvm.org/D125992