[AArch64][SVE] Add new ld<n> intrinsics that return a struct of vscale types

This will allow us to reuse existing interleaved load logic in
lowerInterleavedLoad that exists for neon types, but for SVE fixed
types.

The goal eventually will be to replace the existing ld<n> intriniscs
with these, once a migration path has been sorted out.

Differential Revision: https://reviews.llvm.org/D112078