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/k2g_evm_defconfig b/configs/k2g_evm_defconfig
index c71f67c..8a2dc7f 100644
--- a/configs/k2g_evm_defconfig
+++ b/configs/k2g_evm_defconfig
@@ -30,6 +30,7 @@
 CONFIG_OF_LIST="keystone-k2g-generic keystone-k2g-evm keystone-k2g-ice"
 CONFIG_DTB_RESELECT=y
 CONFIG_MULTI_DTB_FIT=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_DM=y
 # CONFIG_BLK is not set
 CONFIG_DM_MMC=y