Migrate CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG to Kconfig

Convert CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG to Kconfig

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel at gmail.com>
diff --git a/configs/duovero_defconfig b/configs/duovero_defconfig
index c55a93c..23ca1b7 100644
--- a/configs/duovero_defconfig
+++ b/configs/duovero_defconfig
@@ -23,6 +23,7 @@
 CONFIG_CMD_EXT4_WRITE=y
 # CONFIG_SPL_EFI_PARTITION is not set
 CONFIG_SPL_PARTITION_UUIDS=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_NETDEVICES=y
 CONFIG_SMC911X=y