dt-bindings: backlight: Convert zii,rave-sp-backlight.txt to yaml

Convert device tree binding doc zii,rave-sp-backlight.txt to yaml format.
Additional Changes:
- Remove mfd parent node at example.
- Ref to backlight's common.yaml

Signed-off-by: Frank Li <[e-mail]>
Reviewed-by: Daniel Thompson <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/leds/backlight/zii,rave-sp-backlight.txt

···
-Zodiac Inflight Innovations RAVE Supervisory Processor Backlight Bindings
-
-RAVE SP backlight device is a "MFD cell" device corresponding to
-backlight functionality of RAVE Supervisory Processor. It is expected
-that its Device Tree node is specified as a child of the node
-corresponding to the parent RAVE SP device (as documented in
-Documentation/devicetree/bindings/mfd/zii,rave-sp.txt)
-
-Required properties:
-
-- compatible: Should be "zii,rave-sp-backlight"
-
-Example:
-
-	rave-sp {
-		compatible = "zii,rave-sp-rdu1";
-		current-speed = <38400>;
-
-		backlight {
-			compatible = "zii,rave-sp-backlight";
-		};
-	}
-

Documentation/devicetree/bindings/leds/backlight/zii,rave-sp-backlight.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/zii,rave-sp-backlight.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Zodiac Inflight Innovations RAVE Supervisory Processor Backlight
+
+maintainers:
+  - Frank Li <[e-mail]>
+
+description:
+  RAVE SP backlight device is a "MFD cell" device corresponding to
+  backlight functionality of RAVE Supervisory Processor. It is expected
+  that its Device Tree node is specified as a child of the node
+  corresponding to the parent RAVE SP device (as documented in
+  Documentation/devicetree/bindings/mfd/zii,rave-sp.yaml)
+
+properties:
+  compatible:
+    const: zii,rave-sp-backlight
+
+required:
+  - compatible
+
+allOf:
+  - $ref: common.yaml
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    backlight {
+        compatible = "zii,rave-sp-backlight";
+    };
+