sh-pfc: Use sh_pfc_ namespace prefix through the whole driver

Most of the function and structure names are prefixed by sh_pfc_. Fix
the ones that are not to avoid namespace clashes (especially for
functions that start with gpio_).

Not included in this patch are the platform data structures, those will
be reworked later.

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