dt-bindings: leds: pwm: Add default-brightness property

Optional default-brightness property specifies brightness value to be
used if default LED state is on.

Signed-off-by: George Stark <[e-mail]>
Acked-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/leds-pwm.yaml

···
           Maximum brightness possible for the LED
         $ref: /schemas/types.yaml#/definitions/uint32
 
+      default-brightness:
+        description:
+          Brightness to be set if LED's default state is on. Used only during
+          initialization. If the option is not set then max brightness is used.
+        $ref: /schemas/types.yaml#/definitions/uint32
+
     required:
       - pwms
       - max-brightness