sh-pfc: Implement generic pinconf support

The existing PFC pinconf implementation, tied to the PFC-specific pin
types, isn't used by drivers or boards. Replace it with the generic
pinconf types to implement bias (pull-up/down) setup. Other pin
configuration options can be implemented later if needed.

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