[CodeGen] Make MachineInstrBuilder::copyImplicitOps const. NFC.

This matches the other MIB methods, none of which modify the builder.
Without this, we can't chain copyImplicitOps.
Also reformat the few users, in PPCEarlyReturn.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255828 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed