PM: EM: Introduce em_adjust_cpu_capacity()

PM: EM: Introduce em_adjust_cpu_capacity()

Add a function for updating the Energy Model for a CPU after its
capacity has changed, which subsequently will be used by the
intel_pstate driver.

An EM_PERF_DOMAIN_ARTIFICIAL check is added to em_recalc_and_update()
to prevent it from calling em_compute_costs() for an "artificial" perf
domain with a NULL cb parameter which would cause it to crash.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://patch.msgid.link/3637203.iIbC2pHGDl@rjwysocki.net