config: Move CONFIG_DEFAULT_FDT_FILE to defconfigs

- Add DEFAULT_FDT_FILE kconfig entry
- Move CONFIG_DEFAULT_FDT_FILE from include/configs to defconfigs

Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/configs/pico-imx6ul_defconfig b/configs/pico-imx6ul_defconfig
index 1aaf868..dba67bb 100644
--- a/configs/pico-imx6ul_defconfig
+++ b/configs/pico-imx6ul_defconfig
@@ -2,6 +2,7 @@
 CONFIG_ARCH_MX6=y
 CONFIG_TARGET_PICO_IMX6UL=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/technexion/pico-imx6ul/imximage.cfg"
+CONFIG_DEFAULT_FDT_FILE="imx6ul-pico-hobbit.dtb"
 CONFIG_BOOTDELAY=3
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y