[AArch64] Add support for NEON scalar three register different instruction
class.  The instruction class includes the signed saturating doubling
multiply-add long, signed saturating doubling multiply-subtract long, and
the signed saturating doubling multiply long instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192908 91177308-0d34-0410-b5e6-96231b3b80d8