sched/fair: consider task utilization in group_norm_util()

The group_norm_util() function is used to compute the normalized
utilization of a SG given a certain energy_env configuration.
The main client of this function is the energy_diff function when it
comes to compute the SG energy for one of the before/after scheduling
candidates.

Currently, the energy_diff function sets util_delta = 0 when it wants to
compute the energy corresponding to the scheduling candidate where the
task runs in the previous CPU. This implies that, for the task waking up
in the previous CPU we consider only its blocked load tracked by the CPU
RQ. However, in case of a medium-big task which is waking up on a long
time idle CPU, this blocked load can be already completely decayed.

More in general, the current approach is biased towards under-estimating
the energy consumption for the "before" scheduling candidate.

This patch fixes this by:
- always use the cpu_util_wake() to properly get the utilization of a CPU
  without any (partially decayed) contribution of the waking up task
- adding the task utilization to the cpu_util_wake just for the
  target cpu

The "target CPU" is defined by the energy_env to be either the src_cpu
or the dst_cpu, depending on which scheduling candidate we are
considering.

This patch update also the definition of __cpu_norm_util(), which is
currently called just by the group_norm_util() function. This allows to
simplify the code by using this function just to normalize a specified
utilization with respect to a given capacity.

This update allows to completely remove any dependency of
group_norm_util() from calc_util_delta().

Change-Id: I3b6ec50ce8decb1521faae660e326ab3319d3c82
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
(cherry picked from commit ef34ea830347ca175ba8a1baf05357ed98d5728c)
Signed-off-by: Quentin Perret <quentin.perret@arm.com>