cpufreq: brcmstb-avs-cpufreq: properly retrieve P-state upon suspend

The AVS GET_PMAP command does return a P-state along with the P-map
information. However, that P-state is the initial P-state when the
P-map was first downloaded to AVS. It is *not* the current P-state.

Therefore, we explicitly retrieve the P-state using the GET_PSTATE
command.

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