dt-bindings: input: add Coreriver TC360 binding

Signed-off-by: Nick Reitemeyer <nick.reitemeyer@web.de>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200121141525.3404-2-nick.reitemeyer@web.deSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/cypress,tm2-touchkey.txt

@@ -5,6 +5,7 @@ Required properties:
     * "cypress,tm2-touchkey" - for the touchkey found on the tm2 board
     * "cypress,midas-touchkey" - for the touchkey found on midas boards
     * "cypress,aries-touchkey" - for the touchkey found on aries boards
+    * "coreriver,tc360-touchkey" - for the Coreriver TouchCore 360 touchkey
 - reg: I2C address of the chip.
 - interrupts: interrupt to which the chip is connected (see interrupt
 	binding[0]).