Add config option for linking to local CPU in GSN-EDF

Make it possible to turn of the "always link locally if possible"
latency optimization.

This patch also fixes a bug when local linking is used together with
release master support.

Based on a patch by Felipe Cerqueira (felipec@mpi-sws.org).
C-EDF: add support for CONFIG_PREFER_LOCAL_LINKING

Port the "link locally if possible" latency optimization from GSN-EDF
to C-EDF.
/proc/litmus: Export info. on CPU <-> cluster

This patch adds a framework by which plugins can
export information about CPU <-> cluster (aka
scheduling domain) per cluster.

/proc/litmus/domains/<domain#>: This file contains a CPU
mask describing the CPUs scheduled/managed by that domain.
Files are named by index. For example, the first scheduling
domain would be '0'.

/proc/litmus/cpus/<cpus#>: This file contains a domain
mask describing which domains manage this CPU. Normally,
only one bit will be set in this mask, but overlapping clusters
can also be expressed by setting multiple bits.
sched_plgn: Add fn. for reporting CPU/cluster maps

This patch adds the plugin interface "get_domain_proc_info()".
Plugins use this function to report their cpu/clustering configuration
to the user via /proc/litmus/domains and /proc/litmus/cpus.
Set /proc/litmus/cpus (and domains) on plg activ.

This patch updates the plugin activation routine.
Prior to deactivation, a plugin's data for /proc/litmus/cpus
and /proc/litmus/domains is deactivated/removed.
After successful plugin activation, get_domain_proc_info()
is called on the activated plugin, and the resulting info
is used to configure /proc/litmus/cpus and /proc/litmus/domains.
C-EDF: Export cluster configuration to /proc.

This patch updates C-EDF to support get_domain_proc_info().
G-EDF: Export cluster configuration to /proc

This patch updates G-EDF to support get_domain_proc_info().
PSN-EDF: Export cluster configuration to /proc.

This patch updated PSN-EDF to support get_domain_proc_info().
P-FP: Export cluster configuration to /proc.

This patch updated P-FP to support get_domain_proc_info().
PFAIR: Export cluster configuration to /proc.

This patch updated PFAIR to support get_domain_proc_info().