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/mx6dlarm2_defconfig b/configs/mx6dlarm2_defconfig
index 9ba7599..e370c41 100644
--- a/configs/mx6dlarm2_defconfig
+++ b/configs/mx6dlarm2_defconfig
@@ -3,6 +3,7 @@
 CONFIG_TARGET_MX6QARM2=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6qarm2/imximage_mx6dl.cfg,MX6DL,DDR_MB=2048"
 CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set