The driver exposed V4L2_CID_VBLANK as a read only control to allow
for exposure calculations and determination of the frame rate.

Convert to a read/write control so that the frame rate can be
controlled.
V4L2_CID_VBLANK also sets the limits for the exposure control,
therefore exposure ranges have to be updated when vblank changes
(either via s_ctrl, or via changing mode).
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>