AArch64/ARM64: implement "mov $Rd, $Imm" aliases in TableGen.

This is a slightly different approach to AArch64 (the base instruction
definitions aren't quite right for that to work), but achieves the
same thing and reduces C++ hackery in AsmParser.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208605 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64/ARM64: use InstAliases for NEON logical (imm) instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208606 91177308-0d34-0410-b5e6-96231b3b80d8