pinctrl: Move for_each_maps() to namespace and hide iterator inside

First of all, while for_each_maps() is private to pin control subsystem
it's still better to have it put into a namespace.

Besides that, users are not relying on iterator variable, so hide it
inside for-loop.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221111120048.42968-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>