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/MPC8568MDS_defconfig b/configs/MPC8568MDS_defconfig
index c6bc814..370c84f 100644
--- a/configs/MPC8568MDS_defconfig
+++ b/configs/MPC8568MDS_defconfig
@@ -5,6 +5,7 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_STDOUT_VIA_ALIAS=y
 CONFIG_BOOTDELAY=10
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MII=y