The two address pass cannot handle two addr instructions where one incoming

The two address pass cannot handle two addr instructions where one incoming
value is a physreg and one is a virtreg.  For this reason, disable copy folding
entirely for physregs.  Also, use the new isMoveInstr target hook which gives us
folding of FP moves as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11700 91177308-0d34-0410-b5e6-96231b3b80d8