media: dt-bindings: Update bindings for Cadence CSI2TX version 2.1

This patch adds a DT bindings documentation for
Cadence CSI2TX v2.1 controller.

Signed-off-by: Jan Kotas <jank@cadence.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>