cpufreq/cppc: Set the frequency used for computing the capacity

Save the frequency associated to the performance that has been used when
initializing the capacity of CPUs.

Also, cppc cpufreq driver can register an artificial energy model. In such
case, it needs the frequency for this compute capacity.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Pierre Gondois <pierre.gondois@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20231211104855.558096-7-vincent.guittot@linaro.org