dt-bindings: HID: i2c-hid: elan: Introduce Ilitek ili2901

The Ilitek ili2901 touch screen chip same as Elan eKTH6915 controller
has a reset gpio. The difference is that they have different
post_power_delay_ms and post_gpio_reset_on_delay_ms.
Ilitek ili2901 also uses 3.3V power supply.

Signed-off-by: Zhengqiao Xia  <xiazhengqiao@huaqin.corp-partner.google.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Documentation/devicetree/bindings/input/elan,ekth6915.yaml

@@ -18,8 +18,9 @@ allOf:
 
 properties:
   compatible:
-    items:
-      - const: elan,ekth6915
+    enum:
+      - elan,ekth6915
+      - ilitek,ili2901
 
   reg:
     const: 0x10