sched/doc: Factorize bits between sched-energy.rst & sched-capacity.rst

Documentation/scheduler/sched-capacity.rst ought to be the canonical place
to blabber about SD_ASYM_CPUCAPACITY, so remove its explanation from
sched-energy.rst and point to sched-capacity.rst instead.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200731192016.7484-4-valentin.schneider@arm.com

Documentation/scheduler/sched-energy.rst

@@ -331,16 +331,8 @@ asymmetric CPU topologies for now. This requirement is checked at run-time by
 looking for the presence of the SD_ASYM_CPUCAPACITY flag when the scheduling
 domains are built.
 
-The flag is set/cleared automatically by the scheduler topology code whenever
-there are CPUs with different capacities in a root domain. The capacities of
-CPUs are provided by arch-specific code through the arch_scale_cpu_capacity()
-callback. As an example, arm and arm64 share an implementation of this callback
-which uses a combination of CPUFreq data and device-tree bindings to compute the
-capacity of CPUs (see drivers/base/arch_topology.c for more details).
-
-So, in order to use EAS on your platform your architecture must implement the
-arch_scale_cpu_capacity() callback, and some of the CPUs must have a lower
-capacity than others.
+See Documentation/sched/sched-capacity.rst for requirements to be met for this
+flag to be set in the sched_domain hierarchy.
 
 Please note that EAS is not fundamentally incompatible with SMP, but no
 significant savings on SMP platforms have been observed yet. This restriction