dt-bindings: display: st7789v: bound the number of Rx data lines

The ST7789V LCD controller supports regular SPI wiring, as well as no Rx
data line at all. The operating system needs to know whether it can read
registers from the device or not. Let's detail this specific design
possibility by bounding the spi-rx-bus-width property.

Signed-off-by: Miquel Raynal <[email protected]>
Acked-by: Krzysztof Kozlowski <[email protected]>
Reviewed-by: Sebastian Reichel <[email protected]>
Tested-by: Sebastian Reichel <[email protected]>
Signed-off-by: Sebastian Reichel <[email protected]>
Signed-off-by: Neil Armstrong <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: miquelraynal

Documentation/devicetree/bindings/display/panel/sitronix,st7789v.yaml

@@ -29,6 +29,10 @@ properties:
   spi-cpha: true
   spi-cpol: true
 
+  spi-rx-bus-width:
+    minimum: 0
+    maximum: 1
+
   dc-gpios:
     maxItems: 1
     description: DCX pin, Display data/command selection pin in parallel interface