dt-bindings: tda998x: add the calibration gpio

Add the optional calibration gpio for integrated TDA9950 CEC support.
This GPIO corresponds with the interrupt from the TDA998x, as the
calibration requires driving the interrupt pin low.
Reviewed-by: NRob Herring <robh@kernel.org>
Acked-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>

Documentation/devicetree/bindings/display/bridge/tda998x.txt

@@ -27,6 +27,9 @@ Optional properties:
 	in question is used. The implementation allows one or two DAIs. If two
 	DAIs are defined, they must be of different type.
 
+  - nxp,calib-gpios: calibration GPIO, which must correspond with the
+	gpio used for the TDA998x interrupt pin.
+
 [1] Documentation/sound/alsa/soc/DAI.txt
 [2] include/dt-bindings/display/tda998x.h