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/axs103_defconfig b/configs/axs103_defconfig
index 30a4021..7ac2d5f 100644
--- a/configs/axs103_defconfig
+++ b/configs/axs103_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SYS_TEXT_BASE=0x81000000
 CONFIG_DEFAULT_DEVICE_TREE="axs10x"
 CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SYS_PROMPT="AXS# "
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set