sh-pfc: Move platform device and driver to the core

The pinctrl module registers both a platform device and a platform
driver. The only purpose of this awkward construction is to have a
device to pass to the pinctrl registration function.

As a first step to get rid of this hack, move the platform device and
driver from the pinctrl module to the core. The platform device will
then be moved to arch code.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>