media: uapi: h264: clarify expected scaling_list_4x4/8x8 order

Clarify that the expected order of scaling lists should follow the order
they are listed in the H264 standard.

The expected scaling list order,
for 4x4: Intra Y, Intra Cb, Intra Cr, Inter Y, Inter Cb, Inter Cr,
for 8x8: Intra Y, Inter Y, Intra Cb, Inter Cb, Intra Cr, Inter Cr.

Also clarify that the values in a scaling list should be in matrix order,
the same value order that vaapi, vdpau and nvdec use.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>