Add a driver for the Renesas RZ/A1 Interrupt Controller.

This supports using up to 8 external interrupts on RZ/A1, with
configurable sense select.

NMI edge select is not yet supported.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>