media: coda: align internal mpeg4 framebuffers to 16x16 macroblocks

This fixes visual artifacts in the first macroblock row of encoded
MPEG-4 video output caused by 8 additional lines of luma data leaking
into the chroma planes of the internal reference framebuffers: the
buffer size is rounded up to a multiple of 16x16 macroblock size, same
as for the h.264 encoder.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>