[AMDGPU] NFC target dependent requiresUniformRegister refactored out

Summary: Target specific method encapsulated into the Target Lowering Info.

Reviewers: rampitec, vpykhtin

Reviewed By: rampitec

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70085