configs/warp7: Use mainline U-Boot

warp7 is well supported in mainline U-Boot 2016.09, so switch
to this version.

As the current supported kernel is based on a 4.1 kernel from NXP,
use the "warp7_secure" U-Boot target as NXP kernel needs to boot
in secure mode.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

configs/warp7_defconfig

@@ -19,10 +19,9 @@ BR2_LINUX_KERNEL_INTREE_DTS_NAME="imx7s-warp"
 
 # U-Boot
 BR2_TARGET_UBOOT=y
-BR2_TARGET_UBOOT_BOARDNAME="warp7"
-BR2_TARGET_UBOOT_CUSTOM_GIT=y
-BR2_TARGET_UBOOT_CUSTOM_REPO_URL="https://github.com/Freescale/u-boot-fslc.git"
-BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="7a8868eb526b7c1d5dc274bc666bfaef9585ba7c"
+BR2_TARGET_UBOOT_BOARDNAME="warp7_secure"
+BR2_TARGET_UBOOT_CUSTOM_VERSION=y
+BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2016.09"
 BR2_TARGET_UBOOT_FORMAT_IMX=y
 
 # Filesystem