Documentation: drm: bridge: move to video/bridge

Move drm/bridge documentation to video/bridge.
Also, add proper documentation for gpios used by ptn3460.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Tested-by: Rahul Sharma <rahul.sharma@samsung.com>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Tested-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/video/bridge/ptn3460.txt

@@ -3,8 +3,8 @@ ptn3460 bridge bindings
 Required properties:
 	- compatible: "nxp,ptn3460"
 	- reg: i2c address of the bridge
-	- powerdown-gpio: OF device-tree gpio specification
-	- reset-gpio: OF device-tree gpio specification
+	- powerdown-gpio: OF device-tree gpio specification  for PD_N pin.
+	- reset-gpio: OF device-tree gpio specification for RST_N pin.
 	- edid-emulation: The EDID emulation entry to use
 		+-------+------------+------------------+
 		| Value | Resolution | Description      |