[AArch64] Implemented AdvSIMD scalar x indexed element format and AdvSIMD scalar
copy in MC layer. Added the MC layer tests.  Fixed triple setting in test cases.

Patch by Ana Pazos <apazos@codeaurora.org>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194501 91177308-0d34-0410-b5e6-96231b3b80d8