Add support for the V4L2_CID_HBLANK read-only control.

The implementation has been upported from RaspberryPi BSP commit:
commit d82f202156605 ("media: i2c: ov5647: Set V4L2_SUBDEV_FL_HAS_EVENTS flag")
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>