[media] gspca - sonixj: Add exposure, gain and auto exposure for po2030n

The auto gain uses the knee algorithm.
Adding the setexposure control function forced to:
- rename of the previous function setexposure
- add a specific auto setting function

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