sh-pfc: Expose real groups and functions in pinctrl/pinmux operations

The sh-pfc driver exposes one fake group and function per GPIO pin. As
the pinctrl and pinmux APIs are not used by any SuperH and SH Mobile
board or driver, drop the fake groups and functions and replace them by
a real pinctrl and pinmux implementation.

Groups and functions must now be explicitly provided by PFC SoC-specific
data.

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