dt-bindings: i2c: support property idle-state

This supports property idle-state
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Biwen Li <biwen.li@nxp.com>
Signed-off-by: Peter Rosin <peda@axentia.se>

Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt

@@ -25,6 +25,8 @@ Required Properties:
 Optional Properties:
 
   - reset-gpios: Reference to the GPIO connected to the reset input.
+  - idle-state: if present, overrides i2c-mux-idle-disconnect,
+    Please refer to Documentation/devicetree/bindings/mux/mux-controller.txt
   - i2c-mux-idle-disconnect: Boolean; if defined, forces mux to disconnect all
     children in idle state. This is necessary for example, if there are several
     multiplexers on the bus and the devices behind them use same I2C addresses.