Make TargetInstrInfo::copyRegToReg return a bool indicating whether the copy requested

Make TargetInstrInfo::copyRegToReg return a bool indicating whether the copy requested
was inserted or not.  This allows bitcast in fast isel to properly handle the case
where an appropriate reg-to-reg copy is not available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55375 91177308-0d34-0410-b5e6-96231b3b80d8