First part in a series of patches from Dominik which clean up the locking in
cpufreq. It sort of worked, but is full of races. But to keep it
working at least as well it works now, add a new spinlock
cpufreq_driver_lock which will be what cpufreq_driver_sem intended to
be -- but it can indeed be a spinlock instead of a semaphore. 

This driver adds proper protection for struct cpufreq_driver
*cpufreq_driver which can only go away during cpufreq_unregister --
block this by increasing the driver's module reference count.