[AArch64][SVE2] Asm: add integer add/sub long/wide instructions

Summary:
Patch adds support for the following instructions:

SVE2 integer add/subtract long:
    * SADDLB, SADDLT, UADDLB, UADDLT, SSUBLB, SSUBLT, USUBLB, USUBLT,
      SABDLB, SABDLT, UABDLB, UABDLT

SVE2 integer add/subtract wide:
    * SADDWB, SADDWT, UADDWB, UADDWT, SSUBWB, SSUBWT, USUBWB, USUBWT

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

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D62142

llvm-svn: 361615