ENGR00279545 [MX6x:Cpufreq] Initialize mutex before driver registration

ENGR00279545 [MX6x:Cpufreq] Initialize mutex before driver registration

The mutex, set_cpufreq_lock, should be initialized before the driver is
registered. Else if the default governor is set to performance or ondemand,
the cpufreq driver will try to set the freq to the max freq supported and
this will cause a crash during boot.

Signed-off-by: Ranjani Vaidyanathan <ra5478@freescale.com>