colibri_vf: use preboot for fdtfile evaluation

Enable and set preboot var with fdtfile evaluation.
preboot will be checked and run immediately before starting the
CONFIG_BOOTDELAY countdown and/or running the auto-boot command resp.
entering interactive mode.

This provides possibility to use different boot cmds in interactive mode
without manual setting fdtfile value, as it it's already evaluated
before entering interactive mode.

Fixes: 304042c1f3("colibri_vf: set fdtfile for distroboot")
Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>

configs/colibri_vf_defconfig

@@ -11,6 +11,8 @@ CONFIG_TARGET_COLIBRI_VF=y
 CONFIG_DEFAULT_DEVICE_TREE="vf610-colibri"
 CONFIG_ENV_VARS_UBOOT_CONFIG=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/toradex/colibri_vf/imximage.cfg,IMX_NAND"
+CONFIG_USE_PREBOOT=y
+CONFIG_PREBOOT="setenv fdtfile ${soc}-colibri-${fdt_board}.dtb"
 CONFIG_BOOTDELAY=1
 CONFIG_LOGLEVEL=3
 CONFIG_VERSION_VARIABLE=y

include/configs/colibri_vf.h

@@ -76,8 +76,7 @@
 	"ubi read ${fdt_addr_r} dtb && " \
 	"run fdt_fixup && bootz ${kernel_addr_r} - ${fdt_addr_r}\0" \
 
-#define CONFIG_BOOTCOMMAND "run ubiboot; " \
-	"setenv fdtfile ${soc}-colibri-${fdt_board}.dtb && run distro_bootcmd;"
+#define CONFIG_BOOTCOMMAND "run ubiboot || run distro_bootcmd;"
 
 #define BOOT_TARGET_DEVICES(func) \
 	func(MMC, mmc, 0) \