[AMDGPU] Asm/disasm clamp modifier on vop3 int arithmetic

[AMDGPU] Asm/disasm clamp modifier on vop3 int arithmetic

Allow the clamp modifier on vop3 int arithmetic instructions in assembly
and disassembly.

This involved adding a clamp operand to the affected instructions in MIR
and MC, and thus having to fix up several places in codegen and MIR
tests.

Differential Revision: https://reviews.llvm.org/D59267

Change-Id: Ic7775105f02a985b668fa658a0cd7837846a534e

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356399 91177308-0d34-0410-b5e6-96231b3b80d8