dt-bindings: input: touchscreen: elants_i2c: Add compatible for eth3915n chip

This adds a new compatible string for Elan eth3915n touchscreen controller,
which is compatible with ekth3500.
Signed-off-by: Yunlong Jia <ecs.beijing2022@gmail.com>
Suggested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20220923083657.v5.2.Ic4e8f03868f88b8027a81bc3d414bae68978e6b7@changeidSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/elan,elants_i2c.yaml

@@ -14,9 +14,13 @@ allOf:
 
 properties:
   compatible:
-    enum:
-      - elan,ektf3624
-      - elan,ekth3500
+    oneOf:
+      - enum:
+          - elan,ektf3624
+          - elan,ekth3500
+      - items:
+          - const: elan,ekth3915
+          - const: elan,ekth3500
 
   reg:
     maxItems: 1