added support for xio_shutdown - shutdown xio module.
shutdown is symetric call to xio_init

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
use cpufreq if exists to get cpu mhz

If CPU scaling is in use proc may not show the correct CPU MHz
In this case the cycles rate is the maximal frequency and is
take from the virtual file /sys/devices/system/cpu/cpu<N>/cpufreq/scaling_max_freq

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>