rpi3: Enable lan78xx driver

The new Raspberry Pi B 3+ has a lan78xx device attached to it. Let's add
driver support in U-Boot for it.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/configs/rpi_3_defconfig b/configs/rpi_3_defconfig
index 0f3a54e..810b603 100644
--- a/configs/rpi_3_defconfig
+++ b/configs/rpi_3_defconfig
@@ -36,3 +36,5 @@
 CONFIG_CONSOLE_SCROLL_LINES=10
 CONFIG_PHYS_TO_BUS=y
 CONFIG_OF_LIBFDT_OVERLAY=y
+CONFIG_PHYLIB=y
+CONFIG_USB_ETHER_LAN78XX=y