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/cl-som-am57x_defconfig b/configs/cl-som-am57x_defconfig
index eff22bf..53746bf 100644
--- a/configs/cl-som-am57x_defconfig
+++ b/configs/cl-som-am57x_defconfig
@@ -24,6 +24,7 @@
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_SCSI_AHCI=y
 CONFIG_CMD_PCA953X=y
 CONFIG_LED_STATUS=y