ls1088a: remove dhcp function from u-boot env as boot source

Signed-off-by: Pramod Kumar <pramod.kumar_1@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

include/configs/ls1088ardb.h

@@ -455,8 +455,7 @@
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \
-	func(SCSI, scsi, 0) \
-	func(DHCP, dhcp, na)
+	func(SCSI, scsi, 0)
 #include <config_distro_bootcmd.h>
 #endif