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/bg0900_defconfig b/configs/bg0900_defconfig
index 319c3e2..d3afb75 100644
--- a/configs/bg0900_defconfig
+++ b/configs/bg0900_defconfig
@@ -8,6 +8,7 @@
 CONFIG_BOOTDELAY=3
 CONFIG_VERSION_VARIABLE=y
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y