rockchip: evb-rk3339: Enable DHCP

This is the only RK3399 device without DHCP. Enable it so that we
can use a common BOOT_TARGET_DEVICES setting. It is likely useful to be
able to use USB networking, at least. Full networking can be enabled when
a suitable platform needs it.
Signed-off-by: NSimon Glass <sjg@chromium.org>

configs/evb-rk3399_defconfig

@@ -11,6 +11,9 @@ CONFIG_CMD_MMC=y
 CONFIG_CMD_SF=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_CMD_DHCP=y
+CONFIG_CMD_MII=y
+CONFIG_CMD_PING=y
 CONFIG_CMD_TIME=y
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_EXT4=y