[ARM] Fix bogus assertions in copyPhysReg v8.1-M cases.
The code to generate register move instructions in and out of VPR and
FPSCR_NZCV had assertions checking that the other register involved
was a GPR _pair_, instead of a single GPR as it should have been.
Reviewers: miyuki, ostannard
Subscribers: javed.absar, kristof.beyls, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D63865