thermald can disable turbo altogether if needed to avoid reaching
too high operating temperatures, so make the p-state driver monitor
this, and mark the performance mode as inhibited if "no_turbo" is
set.
Closes: #14
The original idea was to have a "SelectedProfile" property that would be
settable by the user, but could be different from the "ActiveProfile" if
the hardware's performance mode wasn't available for example.
It turns out that having 2 separate states makes for very confusing UI,
so if the performance profile becomes inhibited and it's the current one,
the active profile will automatically switch to balanced and stay there.
That allows API users to programmatically check whether a particular
functionality is implemented in the daemon, eg. if we wanted to move
GPU performance modes from gamemode to this daemon, gamemode could
query whether that feature was implemented and available in the backend.
Closes: #12
