cpufreq: arm_big_little: Register an Energy Model

Now that PM_OPP provides a helper function to estimate the power
consumed by CPUs, make sure to try and register an Energy Model (EM)
from the arm_big_little CPUFreq driver, hence ensuring interested
subsystems (the task scheduler, for example) can make use of that
information when available.

Signed-off-by: Dietmar Eggemann <[e-mail]>
Signed-off-by: Quentin Perret <[e-mail]>
Signed-off-by: Viresh Kumar <[e-mail]>

drivers/cpufreq/arm_big_little.c

···
 	policy->cpuinfo.transition_latency =
 				arm_bL_ops->get_transition_latency(cpu_dev);
 
+	dev_pm_opp_of_register_em(policy->cpus);
+
 	if (is_bL_switching_enabled())
 		per_cpu(cpu_last_req_freq, policy->cpu) = clk_get_cpu_rate(policy->cpu);