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/axm_defconfig b/configs/axm_defconfig
index 539e776..0c455fb 100644
--- a/configs/axm_defconfig
+++ b/configs/axm_defconfig
@@ -15,6 +15,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,MACH_TYPE=2068,BOARD_AXM"
 CONFIG_BOOTDELAY=3
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMD_BDI is not set