dt-bindings: bcm: Add Raspberry Pi 3 B+

This adds the root properties for the Raspberry Pi 3 B+
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: NEric Anholt <eric@anholt.net>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NEric Anholt <eric@anholt.net>

Documentation/devicetree/bindings/arm/bcm/brcm,bcm2835.txt

@@ -34,6 +34,10 @@ Raspberry Pi 3 Model B
 Required root node properties:
 compatible = "raspberrypi,3-model-b", "brcm,bcm2837";
 
+Raspberry Pi 3 Model B+
+Required root node properties:
+compatible = "raspberrypi,3-model-b-plus", "brcm,bcm2837";
+
 Raspberry Pi Compute Module
 Required root node properties:
 compatible = "raspberrypi,compute-module", "brcm,bcm2835";