Convert CONFIG_BOARD_EARLY_INIT_F to Kconfig

This converts the following to Kconfig:
   CONFIG_BOARD_EARLY_INIT_F

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/atngw100_defconfig b/configs/atngw100_defconfig
index be48af1..499c329 100644
--- a/configs/atngw100_defconfig
+++ b/configs/atngw100_defconfig
@@ -2,6 +2,7 @@
 CONFIG_MMC=y
 CONFIG_TARGET_ATNGW100=y
 CONFIG_BOOTDELAY=1
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SYS_PROMPT="U-Boot> "
 CONFIG_AUTOBOOT_KEYED=y
 CONFIG_AUTOBOOT_PROMPT="Press SPACE to abort autoboot in %d seconds\n"