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/am43xx_evm_ethboot_defconfig b/configs/am43xx_evm_ethboot_defconfig
index 1bb3395..fcb502c 100644
--- a/configs/am43xx_evm_ethboot_defconfig
+++ b/configs/am43xx_evm_ethboot_defconfig
@@ -34,6 +34,7 @@
 CONFIG_MTDIDS_DEFAULT="nand0=nand.0"
 CONFIG_MTDPARTS_DEFAULT="mtdparts=nand.0:256k(NAND.SPL),256k(NAND.SPL.backup1),256k(NAND.SPL.backup2),256k(NAND.SPL.backup3),512k(NAND.u-boot-spl-os),1m(NAND.u-boot),256k(NAND.u-boot-env),256k(NAND.u-boot-env.backup1),7m(NAND.kernel),-(NAND.file-system)"
 CONFIG_ENV_IS_IN_FAT=y
+CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
 CONFIG_DFU_MMC=y
 CONFIG_DFU_RAM=y
 CONFIG_DFU_SF=y