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

Summary:
Patch adds support for the following instructions:
    * LDNT1SB, LDNT1B, LDNT1SH, LDNT1H, LDNT1SW, LDNT1W, LDNT1D

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

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D62528

llvm-svn: 362072