arm: mvebu: enable two USB interfaces on the Armada XP GP board

The Armada XP GP board has two USB slots: one on the front side and
one on the back side. This commit enables the two USB host controllers
that correspond to those wo USB slots.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>

arch/arm/boot/dts/armada-xp-gp.dts

@@ -101,6 +101,16 @@ ethernet@34000 {
 				phy-mode = "rgmii-id";
 			};
 
+			/* Front-side USB slot */
+			usb@50000 {
+				status = "okay";
+			};
+
+			/* Back-side USB slot */
+			usb@51000 {
+				status = "okay";
+			};
+
 			spi0: spi@10600 {
 				status = "okay";