pinctrl: Re-order pinconf.[ch] to match each-other

Modify the two files so that the order of function prototypes in the
header matches the order of implementations in the .c file.

Don't prototype a couple of internal functions.

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