[SVE][CodeGen] Legalisation of masked loads and stores

Summary:
This patch modifies IncrementMemoryAddress to use a vscale
when calculating the new address if the data type is scalable.

Also adds tablegen patterns which match an extract_subvector
of a legal predicate type with zip1/zip2 instructions

Reviewers: sdesmalen, efriedma, david-arm

Reviewed By: efriedma, david-arm

Subscribers: tschuett, hiraditya, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83137