This adds functionality for the on-board ILSEL IRQs that chain
IRL mode events. Many on-board devices (ethernet, usb, etc.) rely
on ILSEL IRQs directly.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

This adds initial support for the SH-X3 prototype board.
Only simple logic for the IRQ controller and the heartbeat driver
for now.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>