I’ve just tried 2 different 4.14 kernels and neither of them has worked.
The first one I’ve tried is 4.14.73 (I think it was 73). I built it from the source code in your repo, after checking it had the driver code enabled. After that I’ve copied it to the sd card and booted the bpi. The wlp1s0 interface was still there, which means the driver was loaded correctly, and my laptop connected the wireless network without problems, so I assume that hostapd works as expected with this kernel.
The second is the latest 4.14 from your precompiled kernels. Same as above, but this time in a new installation (reasons below). It showed the interface as expected, but the wireless connection was not tested (reasons below).
The problem is that for some reason, the entire networking system breaks with those kernels. I can still see the interfaces, however there are no packets in or out, no DHCP, no pinging from my laptop (via ethernet) to the bpi even when setting a static ip address. The same problem occurs when I try to use other distros like debian or ubuntu.