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/cm_t43_defconfig b/configs/cm_t43_defconfig
index 31da64b..fadf65d 100644
--- a/configs/cm_t43_defconfig
+++ b/configs/cm_t43_defconfig
@@ -41,6 +41,7 @@
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_CMD_MTDPARTS=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_DM=y
 CONFIG_DM_GPIO=y
 CONFIG_MMC_OMAP_HS=y