[AArch64][SVE2] Asm: add saturating multiply-add long instructions
Summary:
Patch adds support for indexed and unpredicated vectors forms of the
following instructions:
- SQDMLALB, SQDMLALT, SQDMLSLB, SQDMLSLT
The specification can be found here:
https://developer.arm.com/docs/ddi0602/latest
Reviewed By: SjoerdMeijer
Differential Revision: https://reviews.llvm.org/D61997
llvm-svn: 361005