pinctrl/lantiq: add functionality to falcon_pinconf_dbg_show

The current code only has a stub for falcon_pinconf_dbg_show.
This patch adds proper functionality.

Signed-off-by: Thomas Langer <thomas.langer@lantiq.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>