Extend the INTC code with ioremap() support V2.

Support INTC controllers that are not accessible through
a 1:1 virt:phys window. Needed by SH-Mobile ARM INTCS.

The INTC code behaves as usual if the io window resource
is omitted. The slow phys->virt lookup only happens during
setup. The fast path code operates on virtual addresses.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>