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/wb50n_defconfig b/configs/wb50n_defconfig
index ce3677b..5b2daae 100644
--- a/configs/wb50n_defconfig
+++ b/configs/wb50n_defconfig
@@ -23,6 +23,7 @@
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
 CONFIG_ENV_IS_IN_NAND=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_BOOTP_BOOTPATH=y
 CONFIG_BOOTP_GATEWAY=y
 CONFIG_BOOTP_HOSTNAME=y