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/gplugd_defconfig b/configs/gplugd_defconfig
index 3b22e6c..e8dda5d 100644
--- a/configs/gplugd_defconfig
+++ b/configs/gplugd_defconfig
@@ -4,6 +4,7 @@
 # CONFIG_MMC is not set
 CONFIG_BOOTDELAY=3
 # CONFIG_DISPLAY_BOARDINFO is not set
+CONFIG_BOARD_EARLY_INIT_F=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_I2C=y