[AMDGPU] Add llvm.amdgcn.set.inactive.chain.arg intrinsic (#71530)

Add a new intrinsic, similar to llvm.amdgcn.set.inactive, but used only
in functions with the `amdgpu_cs_chain` or `amdgpu_cs_chain_preserve`
calling conventions. It allows setting the inactive lanes to those of a
value received as a VGPR argument (whereas llvm.amdgcn.set.inactive
usually takes a constant as the value of the inactive lanes).

Differential Revision: https://reviews.llvm.org/D158604