i#3044 AArch64 SVE: Add Z registers and a simple encoding group.

Created by: fhahn

This patch adds a new register type for scalable vector (Z) registers and encoding/decoding support for the 'SVE Integer Arithmetic - Unpredicated Group' encoding group.

The specification can be found at https://developer.arm.com/docs/ddi0584/latest/arm-architecture-reference-manual-supplement-the-scalable-vector-extension-sve-for-armv8-a

Issue: #3044

Change-Id: I36b1e55b250aca11a9743e12e517edf500fdba4c