[AMDGPU] Refactor VOP3P Profile and AsmParser, NFC

Refactors VOP3P tablegen and the AsmParser for VOP3P
for better extensibility. NFC intended

Reviewed By: rampitec

Differential Revision: https://reviews.llvm.org/D100602

Change-Id: I038e3a772ac348bb18979cdf3e3ae2e9476dd411