sws: add 16bit gbrp formats to packed_16bpc_bswap()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
sws: enable xyz12, this for now is just for swaping between le and be

Needed for fixing fate

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
fate: fix jpeg2000 on big endian

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>