[globalisel][aarch64] Make getCopyMapping() take register banks ID's rather than IsGPR booleans

Summary:
This allows the function to handle architectures with more than two register banks.

Depends on D27978

Reviewers: ab, t.p.northover, rovka, qcolombet

Subscribers: aditya_nandakumar, kristof.beyls, aemerson, rengolin, vkalintiris, dberris, llvm-commits, rovka

Differential Revision: https://reviews.llvm.org/D27339

llvm-svn: 291902