sh-pfc: r8a73a4: GPIO IRQ support

V2 of code to add GPIO -> IRQ mappings to the
PFC table for the r8a73a4 SoC. Requires the IRQs
to be mapped at a fixed location in Linux IRQ
space. The actual IRQs are not handled by the
PFC, instead IRQC is used on r8a73a4.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>