[AMDGPU][llvm-mc] Some refactoring of .td files

Some custom Operands and AsmOperandClasses moved to proper place.
No functional changes.

Differential Revision: http://reviews.llvm.org/D20012

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268780 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed