Is there any option running the board from a 5V source? If now why was the 5V option dropped?
There is no way to run the HiKey board from a 5V power source.
My understanding is it wasn’t built in because under high load, the board can draw more power than a USB connector can deliver. This sort of thing (taking power from a USB port, but pulling more power than it can supply) has caused some other (non-96) boards to be returned to the vendor for being “broken” when in fact the user should just have plugged in an external power supply.