irqchip: renesas-intc-irqpin: DT binding for sense bitfield width

Most Renesas irqpin controllers have 4-bit sense fields, however, some
have different widths. This patch adds a DT binding to optionally
specify such non-standard values.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>