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/platinum_picon_defconfig b/configs/platinum_picon_defconfig
index 71ebc25..186c489 100644
--- a/configs/platinum_picon_defconfig
+++ b/configs/platinum_picon_defconfig
@@ -13,6 +13,7 @@
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,MX6DL"
 CONFIG_BOOTDELAY=3
+CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL=y
 CONFIG_SPL_DMA_SUPPORT=y
 CONFIG_HUSH_PARSER=y