pinctrl: sh-pfc: Accept standard function, pins and groups properties

The "function", "pins" and "groups" pinmux and pinctrl properties have
been standardized. Support them in addition to the custom "renesas,*"
properties. New-style and old-style properties can't be mixed in DT.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>