V4L/DVB: gscpa_sonixb: Differentiate between sensors with a coarse and fine expo ctrl

Some sensors only allow controlling the exposure by changing the clockdiv,
which means that exposure takes pretty large jumps (for example when going
from a div of 1 to 2, the exposure doubles). Use 2 different entries in
the controls array for these 2 different types of exposure (always
disabling one), and;

Add a new autogain algorithm for the coarse exposure case, which normally
changes the gain setting, only touching the exposure setting if the desired
luminance cannot be reached with gain, and after an exposure change once more
first tries gain, etc. Thus avoiding exposure changes, and the resulting
oscilation because of the huge steps these exposure controls take.

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