[ARM] Add tGPRwithpc register class and use it for TBB/THH

[ARM] Add tGPRwithpc register class and use it for TBB/THH

Summary:
TBB and THH allow using a Thumb GPR or the PC as destination operand.
A few machine verifier failures where due to those instructions not
expecting PC as destination operand.

Add -verify-machineinstrs to test/CodeGen/ARM/jump-table-tbh.ll to add
test coverage even if expensive checks are disabled.

Reviewers: MatzeB, t.p.northover, jmolloy

Reviewed By: MatzeB

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

Differential Revision: https://reviews.llvm.org/D34610

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306654 91177308-0d34-0410-b5e6-96231b3b80d8