imx7s-warp: Does not include u-boot on image

It does not include u-boot binary on the image but builds it so user
can have the u-boot if an update is needed.

Signed-off-by: Daiane Angolini <daiane.angolini@nxp.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

conf/machine/imx7s-warp.conf

@@ -7,6 +7,14 @@
 require conf/machine/include/imx-base.inc
 require conf/machine/include/tune-cortexa7.inc
 
+# WaRP uses eMMC boot partition by default and the u-boot inside .sdcard image
+# does not override it. However, build u-boot binary anyway in order to provide
+# a binary to be used if an update is needed.
+# See how-to override eMMC boot partition on the following link
+# http://git.denx.de/?p=u-boot.git;a=blob;f=board/warp7/README
+IMAGE_BOOTLOADER ?= ""
+EXTRA_IMAGEDEPENDS += "u-boot"
+
 MACHINE_FEATURES += " wifi bluetooth"
 
 SOC_FAMILY = "mx7:mx7d"