V4L/DVB (8825): gspca: More controls for pac73xx and new webcam 093a:2624.

-Add usb id for 093a:2624 (pac7302)
-Report some controls to userspace with 7302 only, as they are 7302 only
-Add gain and exposure controls
-Add autogain
-Fix 7302 imaged being mirrored by default

Signed-off-by: Hans de Goede <j.w.r.degoede@hhs.nl>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>