[ARM] Orion: IRQ support

Signed-off-by: Tzachi Perelstein <tzachi@marvell.com>
Reviewed-by: Nicolas Pitre <nico@marvell.com>
Reviewed-by: Lennert Buytenhek <buytenh@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>