[ARM] Put some of the TTI costmodel behind hasNeon calls.

[ARM] Put some of the TTI costmodel behind hasNeon calls.

This puts some of the calls in ARMTargetTransformInfo.cpp behind hasNeon()
checks, now that we have MVE, and updates all the tests accordingly.

Differential Revision: https://reviews.llvm.org/D63447

llvm-svn: 368587