ARM64: print correct aliases for NEON mov & mvn instructions

In all cases, if a "mov" alias exists, it is the canonical form of the
instruction. Now that TableGen can support aliases containing syntax variants,
we can enable them and improve the quality of the asm output.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208874 91177308-0d34-0410-b5e6-96231b3b80d8