pinctrl: sh-pfc: use a saner Kconfig symbol

There is currently a kludge to get the Makefile to move down
to sh-pfc:s drivers: the arch definitions are used twice to
get it done. However we can very well use the Kconfig symbol
for the SH PFC pin control feature itself: it doesn't matter
that it comes from a lower leaf in the Kconfig hierarchy which
is completely orthogonal.

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