[AMDGPU][MC] Fix for Bugs 28200, 28202 + LIT tests

Fixed several related issues with VOP3 fp modifiers.

Reviewers: artem.tamazov

Differential Revision: https://reviews.llvm.org/D30821

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298255 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed