hook-functions: Handle panfrost dependency on governor-simpleondemand

The plymouth hook adds panfrost to the initramfs, but that fails to probe without a devfreq governor. This MR adds one as a hidden dependency, but hidden dependencies are resolved before the hooks are run, so also adjusts the timing of that as well.

We could say it's a hidden dependency of gpu-sched instead, that also works. I chose panfrost over gpu-sched since amdgpu depends on gpu-sched without needing the governor on my amd64 laptop, not sure which is better.

Tested on arm64, amd64. Would be useful for bullseye as well, I forgot I was working around this with a hook. Also see Debian bug #1001039 about this.