[AArch64][SVE] Add SVE2 intrinsics for widening DSP operations

Summary:
Implements the following intrinsics:

 - @llvm.aarch64.sve.[s|u]abalb
 - @llvm.aarch64.sve.[s|u]abalt
 - @llvm.aarch64.sve.[s|u]addlb
 - @llvm.aarch64.sve.[s|u]addlt
 - @llvm.aarch64.sve.[s|u]sublb
 - @llvm.aarch64.sve.[s|u]sublt
 - @llvm.aarch64.sve.[s|u]abdlb
 - @llvm.aarch64.sve.[s|u]abdlt
 - @llvm.aarch64.sve.sqdmullb
 - @llvm.aarch64.sve.sqdmullt
 - @llvm.aarch64.sve.[s|u]mullb
 - @llvm.aarch64.sve.[s|u]mullt

Reviewers: sdesmalen, dancgr, efriedma, cameron.mcinally, rengolin

Reviewed By: sdesmalen

Subscribers: tschuett, kristof.beyls, hiraditya, rkruppe, psnobl, cfe-commits, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73719