gpiolib: Extract gpio_set_config_with_argument_optional() helper

This function is useful for internal use in the GPIO library.
There will be new user coming, prepare a helper for the new comer
and the existing ones.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>