colibri_vf: set fdtfile for distroboot

colibri_vf: set fdtfile for distroboot

Set fdtfile to represent the current board. This allows distribution
to load the correct device tree, which in the module case often
deviates from the common fallback ${soc}-${board}${boardver}.dtb...

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Acked-by: Max Krummenacher <max.krummenacher@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@toradex.com>