[AMDGPU] ISel for llvm.amdgcn.set.inactive.chain.arg

Add patterns to select int_amdgcn_set_inactive_chain_arg to
V_SET_INACTIVE.

This could probably use some more testing, but at least for simple cases
V_SET_INACTIVE seems to mostly work out of the box.

Differential Revision: https://reviews.llvm.org/D158605