[media] gspca_pac7311: Remove vflip control

Enabling vflip leads to a much better image, with vflip disabled the
image looks washed out as if there is a too high brightness setting.

Since we don't know how to lower the brightness setting when not
vflipping, simply always vflip and tell userspace to flip the image back,
resulting in a much better (less washed out) image.

Since the image is now no longer too bright, also modify the luminance
level the auto-gain algorithm aims for.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>