V4L/DVB (8675): gspca: Pixmap PJPG (Pixart 73xx JPEG) added, generated by pac7311.

The JPEG frames generated by the Pixart 73xx have:
- special markers 'ff ff ff xx' every 1024/512 bytes,
- unused 8 bits at end of JPEG blocks,
and then ask for a new pixel format.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>