Make cpufreq module optional for rt-app calibration

Created by: jlelli

If cpufreq module is not used (e.g., KVM target) rt-app calibration should still work as usual, no need to set frequency to max in this case though.

Remove the hard dependecy towards cpufreq module.

Signed-off-by: Juri Lelli juri.lelli@redhat.com