aarch64: vp9itxfm: Reorder the idct coefficients for better pairing

aarch64: vp9itxfm: Reorder the idct coefficients for better pairing

All elements are used pairwise, except for the first one.
Previously, the 16th element was unused. Move the unused element
to the second slot, to make the later element pairs not split
across registers.

This simplifies loading only parts of the coefficients,
reducing the difference to the 16 bpp version.

This is cherrypicked from libav commit
09eb88a12e008d10a3f7a6be75d18ad98b368e68.

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