media: ov5640: Add ov5640_is_csi2() function

Checking if the sensor is used in DVP or MIPI CSI-2 mode is a repeated
pattern which is about to be repeated more often.

Provide an inline function to shortcut that.

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>