ARM: dts: r7s9210: Add IRQC device node

Enable support for the IRQC on RZ/A2M, which is a small front-end to the
GIC.  This allows to use up to 8 external interrupts with configurable
sense select.

Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>