dt-bindings: input: ektf2127: Add elan,ektf2132 compatible string

The eKTF2132 is a touchscreen controller found, for example, in the Kobo
Aura ebook reader. It is similar to the ektf2127, but it uses a different
packet type to report touch events.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20201106112412.390724-2-j.neuschaefer@gmx.netSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/ektf2127.txt

 * Elan eKTF2127 I2C touchscreen controller
 
 Required properties:
- - compatible		  : "elan,ektf2127"
+ - compatible		  : "elan,ektf2127" or "elan,ektf2132"
  - reg			  : I2C slave address of the chip (0x40)
  - interrupts		  : interrupt specification for the ektf2127 interrupt
  - power-gpios		  : GPIO specification for the pin connected to the