[AArch64][Falkor] Fix correctness bug in falkor prefetcher fix pass and...

[AArch64][Falkor] Fix correctness bug in falkor prefetcher fix pass and correct some opcode tag computations.

Summary:
This addresses a correctness bug for LD[1234]*_POST opcodes that have
the prefetcher fix applied to them: the base register was not being
written back from the temp after being incremented, so it would appear
to never be incremented.

Also, fix some opcode tag computations based on some updated HW details
to get better tag avoidance and thus better prefetcher performance.

Reviewers: mcrosier

Subscribers: aemerson, rengolin, javed.absar, kristof.beyls

Differential Revision: https://reviews.llvm.org/D38256

llvm-svn: 314251