configs/mx6cubox: switch uboot to Kconfig build system

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/mx6cubox_defconfig

@@ -30,9 +30,10 @@ BR2_TARGET_ROOTFS_EXT2_4=y
 
 # Bootloaders
 BR2_TARGET_UBOOT=y
-BR2_TARGET_UBOOT_BOARDNAME="mx6cuboxi"
+BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2018.03"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="mx6cuboxi"
 BR2_TARGET_UBOOT_FORMAT_IMG=y
 BR2_TARGET_UBOOT_SPL=y
 BR2_TARGET_UBOOT_SPL_NAME="SPL"