[AArch64]SME2 instructions that use ZTO operand

This patch adds the assembly/disassembly for the following instructions:
  ZERO (ZT0): Zero ZT0.
  LDR (ZT0): Load ZT0 register.
  STR (ZT0): Store ZT0 register.
  MOVT (scalar to ZT0): Move 8 bytes from general-purpose register to ZT0.
       (ZT0 to scalar): Move 8 bytes from ZT0 to general-purpose register.
 Consecutive:
   LUTI2 (single): Lookup table read with 2-bit indexes.
         (two registers): Lookup table read with 2-bit indexes.
         (four registers): Lookup table read with 2-bit indexes.
   LUTI4 (single): Lookup table read with 4-bit indexes.
         (two registers): Lookup table read with 4-bit indexes.
         (four registers): Lookup table read with 4-bit indexes.

The reference can be found here:

https://developer.arm.com/documentation/ddi0602/2022-09

This patch also adds a new register class and operand for zt0
and a another index operand uimm3s8

Differential Revision: https://reviews.llvm.org/D136088