[ARM64] Parse fixed vector lanes properly so that diagnostics can be emitted

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208863 91177308-0d34-0410-b5e6-96231b3b80d8
[ARM64] Improve load/store diagnostics and forbid 32-bit register addresses

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208864 91177308-0d34-0410-b5e6-96231b3b80d8