media: Introduce helpers to fill pixel format structs

Add two new API helpers, v4l2_fill_pixfmt and v4l2_fill_pixfmt_mp,
to be used by drivers to calculate plane sizes and bytes per lines.

Note that driver-specific padding and alignment are not
taken into account, and must be done by drivers using this API.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>