[AArch64] Avoid NEON ORR when NEON and SVE are unavailable (#93940)

For streaming-compatible functions with only +sme, we can't use
a NEON ORR (aliased as 'mov') for copies of Q-registers, so
we need to use a spill/fill instead.

This also fixes the fill, which should use the post-incrementing
addressing mode.