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/ap121_defconfig b/configs/ap121_defconfig
index d21fa04..91ebb3b 100644
--- a/configs/ap121_defconfig
+++ b/configs/ap121_defconfig
@@ -4,6 +4,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="ap121"
 CONFIG_BOOTDELAY=3
 CONFIG_DISPLAY_CPUINFO=y
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SYS_PROMPT="ap121 # "
 # CONFIG_CMD_BDI is not set
 # CONFIG_CMD_CONSOLE is not set