sh: Support SCHED_MC for SH-X3 multi-cores.

This enables SCHED_MC support for SH-X3 multi-cores. Presently this is
just a simple wrapper around the possible map, but this allows for
tying in support for some of the more exotic NUMA clusters where we can
actually do something with the topology.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>