[AArch64][SVE2] Asm: support SVE2 store instructions

Summary:
Patch adds support for the following instructions:
    * STNT1B, STNT1H, STNT1S, STNT1D

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

Reviewed By: chill

Differential Revision: https://reviews.llvm.org/D62599

llvm-svn: 362213