MLK-14480 mx7ulp_evk: Add netboot to default boot command

Add netboot to CONFIG_BOOTCOMMAND, so when loadimage from SD fails,
it can continue to boot from network.

Signed-off-by: Ye Li <ye.li@nxp.com>
(cherry picked from commit c1c23ff6)

include/configs/mx7ulp_evk.h

@@ -234,6 +234,7 @@
 		   "else " \
 			   "if run loadimage; then " \
 				   "run mmcboot; " \
+			   "else run netboot; " \
 			   "fi; " \
 		   "fi; " \
 	   "fi"