scmi-cpufreq: Get opp_shared_cpus from opp-v2 for EM

By design, SCMI performance domains define the granularity of
performance controls, they do not describe any underlying hardware
dependencies (although they may match in many cases).

It is therefore possible to have some platforms where hardware may have
the ability to control CPU performance at different granularity and choose
to describe fine-grained performance control through SCMI.

In such situations, the energy model would be provided with inaccurate
information based on controls, while it still needs to know the
performance boundaries.

To restore correct functionality, retrieve information of CPUs under the
same performance domain from operating-points-v2 in DT, and pass it on to
EM.

Link: https://lore.kernel.org/r/20210218222326.15788-3-nicola.mazzucato@arm.com


Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>