sh: intc: install enable, disable and shutdown callbacks

Modify the intc code to install a disable callback. The current
solution without a disable callback results in use of the
generic default_disable() function. This function is a no-op
so suspend_device_irqs() will not disable any intc interrupts
at suspend time without this patch. Also, install enable and
shutdown callbacks while at it.

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