ANDROID: sched/fair: add arch scaling function for max frequency capping

To be able to scale the cpu capacity by this factor introduce a call to
the new arch scaling function arch_scale_max_freq_capacity() in
update_cpu_capacity() and provide a default implementation which returns
SCHED_CAPACITY_SCALE.

Another subsystem (e.g. cpufreq) or architectural or platform specific
code can overwrite this default implementation, exactly as for frequency
and cpu invariance. It has to be enabled by the arch by defining
arch_scale_max_freq_capacity to the actual implementation.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
( Fixed conflict with scaling against the PELT-based scale_rt_capacity )
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
Change-Id: I770a8b1f4f7340e9e314f71c64a765bf880f4b4d