There are currently two drivers in the 3rd Party drivers repo: indi-asi-power and indi-rpi-gpio which would both do the job. The first one is specifically set up for the ASIAir Pro whilst the second one is more generalised for any RPi so the GPIO pinds are configurable.
There is currently an issue with the builds on these as they are dependent on the build of the libpigpiod library but I'm not able to get that library to build automatically. I'm sure it is not complicated but I've never done it so don't know specifically what is needed. If any other dev knows how, we can probably sort out the issues pretty quickly and make those drivers available in the nightly builds.