[AArch64][SVE] Implement reversal intrinsics

Summary:
Adds intrinsics for the following:

    * rbit
    * revb
    * revh
    * revw

Patterns are also defined to map the 'llvm.bswap.*' intrinsic to the SVE
revb instruction.

Reviewers: sdesmalen, huntergr, dancgr, rengolin, efriedma, rovka

Reviewed By: sdesmalen

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70960