[ANDGPU] getMemOperandsWithOffset: support BUF non-stack-access instructions...

[ANDGPU] getMemOperandsWithOffset: support BUF non-stack-access instructions with resource but no vaddr

Summary:
This enables clustering for many more BUF instructions.

Reviewers: rampitec, arsenm, nhaehnle

Subscribers: jvesely, wdng, hiraditya, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73868