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/mpc5121ads_defconfig b/configs/mpc5121ads_defconfig
index fff0e9b..90d0f46 100644
--- a/configs/mpc5121ads_defconfig
+++ b/configs/mpc5121ads_defconfig
@@ -4,6 +4,7 @@
 CONFIG_TARGET_MPC5121ADS=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=5
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_I2C=y