sched: Allocate eas_cache when EAS is enabled

In find_energy_efficient_cpu(), the energy consumption of each
perf_domain is computed without (base energy) and with
(placed on the max_spare_cap_cpu) the task placed in the perf_domain.
If the prev_cpu of the task is available, it is also considered.

To compute the power consumption of a perf_domain, the frequency
utilization, used to predict the OPP of the perf_domain is computed.
An energy utilization is also computed, representing the time spent
running by the CPU.

For each perf_domain, for each power estimation, these two
utilization values are re-computed, although being invariant when the
task is not placed on the probed CPU.

This patch allocates a cache when EAS is enabled to allow the
find_energy_efficient_cpu() function to save these two utilization
values and re-use them.

Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>