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/mx6sabresd_defconfig b/configs/mx6sabresd_defconfig
index a56d685..c2d1cd4 100644
--- a/configs/mx6sabresd_defconfig
+++ b/configs/mx6sabresd_defconfig
@@ -51,6 +51,7 @@
 CONFIG_CMD_FS_GENERIC=y
 CONFIG_EFI_PARTITION=y
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_FSL_ESDHC=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y