from Dmitry Torokhov.

I have the following problems with ACPI P-States driver:

- It crashes because it tries to switch CPU speed without registering cpufreq
driver first but acpi_processor_set_performance calls cpufreq_notify_transition.

- When testing for capable CPUs it skips all online ones so for my single CPU
notebook it can't activate at all.

- If a processor does not support throttling then it will say that "limit"
interface is not supported even after activating performance control.

The patch below should fix these issues. It also adds some info messages since
/proc/acpi/processor/*/performance interface is marked obsolete but i still
would like to see if P-states were recognized during boot.