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/birdland_bav335b_defconfig b/configs/birdland_bav335b_defconfig
index 21fecde..4f814e4 100644
--- a/configs/birdland_bav335b_defconfig
+++ b/configs/birdland_bav335b_defconfig
@@ -42,6 +42,7 @@
 CONFIG_CMD_USB_MASS_STORAGE=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_EXT4_WRITE=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_DFU_MMC=y
 CONFIG_DFU_RAM=y