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/v38b_defconfig b/configs/v38b_defconfig
index e5dd07a..7fde07f 100644
--- a/configs/v38b_defconfig
+++ b/configs/v38b_defconfig
@@ -3,6 +3,7 @@
 CONFIG_MPC5xxx=y
 CONFIG_TARGET_V38B=y
 CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set