rockchip: Add PXE and DHCP to the default boot targets

Now that at least on the firefly board we have network support, enable
PXE and DHCP boot targets by default.
Signed-off-by: NSjoerd Simons <sjoerd.simons@collabora.co.uk>
Acked-by: NSimon Glass <sjg@chromium.org>
Acked-by: NJoe Hershberger <joe.hershberger@ni.com>

include/configs/rockchip-common.h

@@ -14,7 +14,9 @@
 /* First try to boot from SD (index 0), then eMMC (index 1 */
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \
-	func(MMC, mmc, 1)
+	func(MMC, mmc, 1) \
+	func(PXE, pxe, na) \
+	func(DHCP, dchp, na)
 
  /* Enable gpt partition table */
 #define CONFIG_CMD_GPT