Hello my friend,
I exactly do have your problem. I was working to get the desktop working couple of months ago but because at that time only the server functionality was important to me, I ignored the issue or somehow I gave up.
But now, I backed and want to find out why the Desktop does not work on my HiKey.
I read somewhere that the Mali Driver cause the issue even for Frame buffer. Not sure maybe, but I haven't found the approved Mali Driver Source to compile and test for HiKey.
Found that you also have the same issue. May I ask you if you have found any solution?
If you like we can discuss and see if we can solve this common issue.
I am not sure if your HiKey is from LeMaker or not. However, I think this forum is much better to dicuss this as people have this board in this forum are more than others: http://forum.lemaker.org/forum.php?gid=147