media: i2c: imx290: Convert V4L2_CID_HBLANK to read/write

Should be upstream commit 8cab2bd86307

The driver exposed V4L2_CID_HBLANK 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.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>