pinctrl: ifdef CONFIG_DEBUG_FS cleanup

Only provide prototypes for pin{mux,conf}.c debugfs-related functions
when both CONFIG_PIN* /and/ CONFIG_DEBUG_FS are enabled, otherwise
provide static inlines.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>