The power resource dependencies for each `_PRx` object are discovered and cached in `ac_prx` on the power consumer struct (`struct acpi_powerconsumer`) when a power consumer is registered. This is done in `acpi_pwr_get_power_resources`. This discovery process also registers those power resources, which were previously only registered when they were referenced by the relevant `_PRx` object for the target D-state when switching. This meant that the first D-state switch for a power consumer would not turn off any power resources as they wouldn't have been registered yet. This revision fixes this.
Sponsored by: The FreeBSD Fondation