[BPI-64] how to use dtoverlay with fit

Hi

On old bootchain i had separate dtb file which can be merged with dt-overlays in uboot. With the “new” fit image,the dtb is again builtin,so i cannot load it separately for mwrging with dto.

I found a way to integrate dto into fit,but i search for a way to load separate dto,so user needs only compile dto and not kernel/fit

Any idea how to archive this? @sam33 @ryder.lee

Regards Frank