[AArch64][SVE2] Asm: support SVE2 String Processing Group

Summary:
Patch adds support for the SVE2 character match instructions MATCH and NMATCH.

The specification can be found here:
https://developer.arm.com/docs/ddi0602/latest

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D62206

llvm-svn: 361627