dt-bindings: HID: i2c-hid: elan: add Elan eKTH5015M

Add a compatible string for the Elan eKTH5015M touch controller.

Judging from the current binding and commit bd3cba00dcc6 ("HID: i2c-hid:
elan: Add support for Elan eKTH6915 i2c-hid touchscreens"), eKTH5015M
appears to be compatible with eKTH6915. Notably the power-on sequence is
the same.

While at it, drop a redundant label from the example.

Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Johan Hovold <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Benjamin Tissoires <[e-mail]>

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

···
 
 properties:
   compatible:
-    enum:
-      - elan,ekth6915
+    oneOf:
+      - items:
+          - enum:
+              - elan,ekth5015m
+          - const: elan,ekth6915
+      - const: elan,ekth6915
 
   reg:
     const: 0x10
···
       #address-cells = <1>;
       #size-cells = <0>;
 
-      ap_ts: touchscreen@10 {
-        compatible = "elan,ekth6915";
+      touchscreen@10 {
+        compatible = "elan,ekth5015m", "elan,ekth6915";
         reg = <0x10>;
 
         interrupt-parent = <&tlmm>;