media: gspca_zc3xx: Implement proper autogain and exposure control for OV7648

The ZS0211 internal autogain causes pumping and flickering with OV7648
sensor on 0ac8:307b webcam.
Implement OV7648 autogain and exposure control and use that instead.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>