[AArch64][SVE] Fix selection failure during lowering of shuffle_vector

The lowering code for shuffle_vector has a code path that looks through
extract_subvector, this code path did not properly account for the
potential presense of larger than Neon vector types and could produce
unselectable DAG nodes.

Differential Revision: https://reviews.llvm.org/D119252

(cherry picked from commit 98936aee)