[AMDGPU] Add `.workgroup_processor_mode` to v5 MD

Adds Workgroup Processor Mode (WGP) to the HSA Metadata for Code Object v5/GFX10+.
The field is already present as an asm directive and in the compute program resource register but is also needed in the MD.

Reviewed By: kzhuravl

Differential Revision: https://reviews.llvm.org/D139931