board: Enable DHCP distro boot for LS1012a, LS1021a

Enable DHCP distro boot for Layerscape LS1012A and LS1021A.

Signed-off-by: Yunfeng Ding <yunfeng.ding@nxp.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
diff --git a/include/configs/ls1021atwr.h b/include/configs/ls1021atwr.h
index 2c91ae7..4b6760b 100644
--- a/include/configs/ls1021atwr.h
+++ b/include/configs/ls1021atwr.h
@@ -315,7 +315,8 @@
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \
-	func(USB, usb, 0)
+	func(USB, usb, 0) \
+	func(DHCP, dhcp, na)
 #include <config_distro_bootcmd.h>
 
 #ifdef CONFIG_LPUART