sh: intc - initial SMP support.

This implements initial support for the SMP INTC (particularly
INTC2) controllers.

These are largely implemented as conventional blocks, with
register sets grouped together at fixed strides relative to
the CPU id.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>