cpuidle: psci: Extend information in log about OSI/PC mode

It's useful to understand whether we are using OS-initiated (OSI) mode or
Platform Coordinated (PC) mode, when initializing the CPU PM domains.
Therefore, let's extend the print in the log after a successful probe with
this information.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>