dt-bindings: u-boot: Add property for LED boot and activity

Add property for LED boot and activity and period for blink mode.

These property define the phandle to an LED to use for the u-boot boot or
activity LED to signal successful boot or activity like flash write or
tftp traffic.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

dtschema/schemas/options/u-boot.yaml

@@ -110,6 +110,26 @@ properties:
         enabled)
       2: console output is suppressed and not recorded
 
+  boot-led:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description: |
+      This is used to specify a phandle to an LED to indicate a successful boot.
+
+  boot-led-period-ms:
+    default: 250
+    description: |
+      This is used to specify the default period (in ms) for an LED in blink mode.
+
+  activity-led:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description: |
+      This is used to specify a phandle to an LED to indicate an activity.
+
+  activity-led-period-ms:
+    default: 250
+    description: |
+      This is used to specify the default period (in ms) for an LED in blink mode.
+
 required:
   - compatible