sh: Break out SuperH PFC code

This file breaks out the SuperH PFC code from
arch/sh/kernel/gpio.c + arch/sh/include/asm/gpio.h
to drivers/sh/pfc.c + include/linux/sh_pfc.h.

Similar to the INTC stuff. The non-SuperH specific
file location makes it possible to share the code
between multiple architectures.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>