[globalisel] Initialize RegisterBanks with static data.

Summary:
Refactor the RegisterBank initialization to use static data. This requires
GlobalISel implementations to rewrite calls to createRegisterBank() and
addRegBankCoverage() into a call to setRegBankData().

Out of tree targets can use diff 4 of D27807
(https://reviews.llvm.org/D27807?id=84117) to have addRegBankCoverage() dump
the register classes and other data that needs to be provided to
setRegBankData(). This is the method that was used to generate the static data
in this patch.

Tablegen-eration of this static data will follow after some refactoring.

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

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

Differential Revision: https://reviews.llvm.org/D27807
Differential Revision: https://reviews.llvm.org/D27808

llvm-svn: 291768