<Dominik Brodowski>

Too many users use the p4-clockmod cpufreq driver instead of the more
advanced speedstep-centrino, speedstep-ich or even acpi drivers. All of the
latter (usually) provide voltage scaling, while the p4-clockmod driver only
offers a variant of frequency scaling. So, warn users if they try out this
driver instead.
                                                                                               
Also, instead of using a local copy, use the speedstep_lib infrastructure
for detecting the processor speed. Adding the Pentium-M get_frequency
function to that module only costs about 200 bytes in object size.