bcm281xx: enable CONFIG_OF_LIBFDT

set the Kconfig parameter: CONFIG_OF_LIBFDT

Signed-off-by: Steve Rae <srae@broadcom.com>
diff --git a/configs/bcm28155_ap_defconfig b/configs/bcm28155_ap_defconfig
index ba57944..538647d 100644
--- a/configs/bcm28155_ap_defconfig
+++ b/configs/bcm28155_ap_defconfig
@@ -9,3 +9,4 @@
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_USB_GADGET=y
+CONFIG_OF_LIBFDT=y