media: dt-bindings: imx7-csi: add i.MX6UL/L support

Document "fsl,imx6ul-csi" entry.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>