dt-bindings: display: panel: mipi-dbi-spi: add spi-3wire property

Some MIPI DBI panels support a three wire mode (clock, chip select,
bidirectional data) that can be used to ask the panel if it is already set
up by e.g. the bootloader and can thus skip the initialization.
This enables a flicker-free boot.

Signed-off-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://lore.kernel.org/r/20230614123222.4167460-4-l.goehrs@pengutronix.de
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml

@@ -87,6 +87,8 @@ properties:
       Logic level supply for interface signals (Vddi).
       No need to set if this is the same as power-supply.
 
+  spi-3wire: true
+
 required:
   - compatible
   - reg