[media] v4l: Documentation about the JPGL pixel format

The JPG-Light, AKA Pegasus Lossless JPEG, is used in Divio webcams based
on NW 800/801/802 chips.

Signed-off-by: Jean-François Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>