ARM: sa1111: use an irqdomain for SA1111 interrupts

Use an IRQ domain for SA1111 interrupts, which allows us to separate the
hardware interrupt number from the Linux interrupt number.  We can then
use the hardware interrupt number stored in the irq_data to calculate
the register offsets and mask.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>