sh-pfc: Add entries for INTC external IRQs

We add all necessary entries to support the external IRQs from the INTC.

Signed-off-by: Bastian Hecht <hechtb+renesas@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>