Adds some more code to GlobalISel to enable instruction selection for and/or/xor.
- Makes G_IMPLICIT_DEF, G_CONSTANT, G_AND, G_OR, G_XOR legal for 64bit register size.
- Implement lowerReturn in CallLowering
- Provides mapping of the operands to register banks.
- Adds register info to G_COPY operands.
The utility functions are all only implemented so far to support this use case.
Especially the functions in PPCGenRegisterBankInfo.def are too simple for
general use.
Reviewed By: nemanjai, shchenz, amyk
Differential Revision: https://reviews.llvm.org/D127530
