[TwoAddressInstructionPass] Improve tryInstructionCommute of X86 FMA and vpternlog instructions

These instructions have 3 operands that can be commuted. The first commute we find may not be the best. So we should keep searching if we performed an aggressive commute. There may still be an operand that is killed or a physical register constraint that might be better.

Differential Revision: https://reviews.llvm.org/D44324

llvm-svn: 327188