sched: IRMOS-only changes, EDF stats and multi-CPU interface

This patch is not intended for mainline submission, it contains extensions
developed in the context of the IRMOS EU project:

  - export EDF statistics and parameters;
  - allow configuring independently runtime and period on multiple CPUs.

Signed-off-by: Fabio Checconi <fchecconi@gmail.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>