[CPUFREQ] Make powernow-k7 work on SMP kernels.

Even though powernow-k7 doesn't work in SMP environments,
it can work on an SMP configured kernel if there's only
one CPU present, however recalibrate_cpu_khz was returning
-EINVAL on such kernels, so we failed to init the cpufreq driver.

Signed-off-by: Dave Jones <davej@redhat.com>