media: imx: De-stage imx7-mipi-csis

The imx7-mipi-csis driver is in a good state and can be destaged.

Move the imx7-mipi-csis.c driver to the newly created
drivers/media/platform/imx directory and plumb the related
options in Kconfig and in Makefile.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>