arm64: defconfig: Enable CONFIG_ENERGY_MODEL

The recently introduced Energy Model (EM) framework manages power cost
tables for the CPUs of the system. Its only user right now is the
scheduler, in the context of Energy Aware Scheduling (EAS).

However, the EM framework also offers a generic infrastructure that
could replace subsystem-specific implementations of the same concepts,
as this is the case in the thermal framework.

So, in order to prepare the migration of the thermal subsystem to use
the EM framework, enable it in the default arm64 defconfig, which is the
most commonly used architecture for IPA. This will also compile-in all
of the EAS code, although it won't be enabled by default -- EAS requires
to use the 'schedutil' CPUFreq governor while arm64 defaults to
'performance'.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20191030151451.7961-2-qperret@google.com