gpiolib: Introduce for_each_gpio_desc_with_flag() macro

In a few places we are using a loop against all GPIO descriptors
with a given flag for a given device. Replace it with a consolidated
for_each type of macro.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>