[AArch64][SVE2] Add SVE2 target features to backend and TargetParser

Summary:
This patch adds the following features defined by Arm SVE2 architecture
extension:

  sve2, sve2-aes, sve2-sm4, sve2-sha3, bitperm

For existing CPUs these features are declared as unsupported to prevent
scheduler errors.

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

Reviewers: SjoerdMeijer, sdesmalen, ostannard, rovka

Reviewed By: SjoerdMeijer, rovka

Subscribers: rovka, javed.absar, tschuett, kristof.beyls, kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61513

llvm-svn: 360573