aarch64: vp9itxfm: Use a single lane ld1 instead of ld1r where possible

The ld1r is a leftover from the arm version, where this trick is
beneficial on some cores.

Use a single-lane load where we don't need the semantics of ld1r.

This is cherrypicked from libav commit
ed8d2933.

Signed-off-by: Martin Storsjö <martin@martin.st>