dt-bindings: input: microchip,cap11xx: Add microchip,cap1126 LED reg constraints

Apply per-chip LED channel limits:
- CAP1126: max 2 channels (0-1)
- CAP1188: max 8 channels (0-7)
- CAP1106, CAP12xx: no LED support

Signed-off-by: Jun Yan <jerrysteve1101@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260617150318.753148-5-jerrysteve1101@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/microchip,cap11xx.yaml

@@ -171,6 +171,19 @@ allOf:
       patternProperties:
         "^led@": false
 
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - microchip,cap1126
+    then:
+      patternProperties:
+        "^led@":
+          properties:
+            reg:
+              maximum: 1
+
   - if:
       properties:
         compatible: