V4L/DVB (9877): gspca - ov534: Add framerate support.

Add support for getting and setting framerate via v4l2 controls,
rather than setting a fixed value at module insertion.

Signed-off-by: Jim Paris <jim@jtan.com>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>