pinctrl: sh-pfc: Get rid of CONFIG_ARCH_SHMOBILE_LEGACY

Shmobile is all multiplatform these days, so get rid of the reference to
CONFIG_ARCH_SHMOBILE_LEGACY.

Move the legacy code to do the non-DT mapping between GPIOs and pins
inside the existing #ifdef CONFIG_SUPERH section.

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