Add INTCS support for the sh73a0 processor.

The interrupts on the sh73a0 processor are managed
through controllers such as GIC, INTCS and INTCA.

The ARM cores use the GIC as primary interrupt
controller and the INTCS and INTCA are hanging off
the GIC as cascaded interrupt controllers.

Peripherals connected both to the GIC and the INTC
controllers should if possible only use the GIC.

If no GIC connection is available then INTCS and
INTCA may be used instead.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>