[AArch64][SVE] Add SVE2 intrinsics for bit permutation & table lookup

Summary:
Implements the following intrinsics:
 - @llvm.aarch64.sve.bdep.x
 - @llvm.aarch64.sve.bext.x
 - @llvm.aarch64.sve.bgrp.x
 - @llvm.aarch64.sve.tbl2
 - @llvm.aarch64.sve.tbx

The SelectTableSVE2 function in this patch is used to select the TBL2
intrinsic & ensures that the vector registers allocated are consecutive.

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

Reviewed By: efriedma

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74912