media: doc: pixfmt-packed-yuv: Express 4:4:4 formats in a more compact way

The 4:4:4 packed YUV formats are documented with a bit-level
representation, which creates a wide table. Switch to a byte-oriented
representation to make it more compact. This prepares for the addition
of formats with more than 8 bits per component, that would make the
table way too wide.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>