[AArch64] Add additional extract-extend patterns for smov

[AArch64] Add additional extract-extend patterns for smov

This patch adds to the target description two additional patterns for matching
extract-extend operations to SMOV. The patterns catch the v16i8-to-i64 and
v8i16-to-i64 cases. The existing patterns miss these cases because the
extracted elements must first be legalized to i32, resulting in any_extend
nodes.

This was originally implemented as a DAG combine (r255895), but was reverted
due to failing out-of-tree tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256176 91177308-0d34-0410-b5e6-96231b3b80d8