Move unit test to the proper location

Summary: Move test/CodeGen/AArch64/reg-bank-128bit.mir to test/CodeGen/AArch64/GlobalISel/reg-bank-128bit.mir so that the test is executed only when global-isel is enabled. lit.local.cfg under test/CodeGen/AArch64/GlobalISel checks if 'global-isel' is in the available_features while the same file under test/CodeGen/AArch64 doesn't.

Reviewers: qcolombet, davide

Reviewed By: davide

Subscribers: davide, aemerson, javed.absar, igorb, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D36282

llvm-svn: 309985