sched/tune: use a single initialisation function

With the introduction of initialization function required to compute the
energy normalization constants from DTB at boot time, we have now a
late_initcall which is already used by SchedTune.

This patch consolidate within that function the other initialization
bits which was previously deferred to the first CGroup creation.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>