media: ov5640: Add VBLANK control

Add the VBLANK control which allows to select the duration of the
frame vertical blankings and allows to control the framerate.

The VBLANK control also modifies the exposure time range, which cannot
exceed the maximum frame length.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>