RFC measure speedstep-ich transition latency at CPU initialization

Hello,
a foreword: this is my first patch here, it surely needs more work but I'd appreciate some comments before going too far on the wrong lane. Oh, I'm also trying to use some git automation to send the patch, hopefully you won't receive too many dups :)

The 2 patches are trying to implement the suggested runtime measurement of transition latency on speedstep ich chipsets to offer the allow the usage of the dynamic governors to ICH[234]-M owners (like me).

The first patch moves away PMBASE reading and only performs it at cpufreq_register_driver time by exiting with -ENODEV if unable to read the value. (git seems a little confused, I hope it's readable)

The second patch (could be split in 2 if necessary) introduces __speedstep_set_state that performs the frequency transition without disabling interrupts to be used in speedstep_measure_latency and speedstep_get_freqs (IRQs are already disabled here).
It also implements the transition measurement if the parameter 'measure_latency' is set to a value other than 0.

The measurement is performed by means of do_gettimeofday as suggested by Mr. Pallipadi.

Known problems:
- the patch is still missing a sanity check on the measured value
- it also introduces 2 more transitions at init time (2 in speedstep_get_freqs + 2 in speedstep_measure_latency) because I don't know if makes sense to rely (and hack) on speedstep_get_freqs to perform measurements.

thanks
--
mattia
:wq!