cpufreq: ARM big LITTLE: Improve print message

The message printed at the end of driver->init() doesn't include the
"cpufreq" string at all and so is difficult to find in dmesg. Add
function name to that message to clearly state where the message is
coming from.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>