dt-bindings: display: tfp410: Add bus-width parameter property

tfp410 can be connect to host processor in 24bit, single-edge (24 lines) or
12bit, dual-edge (12 lines).

Add bus-width to the documentation so it can be used to select between the
two connection scheme.

Signed-off-by: Peter Ujfalusi <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Andrzej Hajda <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/devicetree/bindings/display/bridge/ti,tfp410.txt

···
 graph bindings specified in [1]. Each port node shall have a single endpoint.
 
 - Port 0 is the DPI input port. Its endpoint subnode shall contain a
-  pclk-sample property and a remote-endpoint property as specified in [1].
+  pclk-sample and bus-width property and a remote-endpoint property as specified
+  in [1].
+  - If pclk-sample is not defined, pclk-sample = 0 should be assumed for
+    backward compatibility.
+  - If bus-width is not defined then bus-width = 24 should be assumed for
+    backward compatibility.
+    bus-width = 24: 24 data lines are connected and single-edge mode
+    bus-width = 12: 12 data lines are connected and dual-edge mode
 
 - Port 1 is the DVI output port. Its endpoint subnode shall contain a
   remote-endpoint property is specified in [1].
···
 
 			tfp410_in: endpoint@0 {
 				pclk-sample = <1>;
+				bus-width = <24>;
 				remote-endpoint = <&dpi_out>;
 			};
 		};