[AMDGPU][NFC] Skip processing intrinsics that do not become real instructions

Reviewers: rampitec

Reviewed By: rampitec

Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81260