jpeg2000dec: Support non subsampled 9-16bit planar pixel formats

This applies changes similar to fc6de70c44be05eb0368ab519bfb790431d8dee5
to the >8bit codepath

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowdec: remove assert.h include, its unused

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/snowenc: convert speed relevant asserts to av_assert2()

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