Currently a genpd only handles the performance state requirements from
the devices under its control. This commit extends that to also handle
the performance state requirement(s) put on the master genpd by its
sub-domains. There is a separate value required for each master that
the genpd has and so a new field is added to the struct gpd_link
(link->performance_state), which represents the link between a genpd and
its master. The struct gpd_link also got another field
prev_performance_state, which is used by genpd core as a temporary
variable during transitions.

On a call to dev_pm_genpd_set_performance_state(), the genpd core first
updates the performance state of the masters of the device's genpd and
then updates the performance state of the genpd. The masters do the same
and propagate performance state updates to their masters before updating
their own. The performance state transition from genpd to its master is
done with the help of dev_pm_opp_xlate_performance_state(), which looks
at the OPP tables of both the domains to translate the state.
Tested-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>