gpiolib: Introduce for_each_requested_gpio_in_range() macro

Introduce for_each_requested_gpio_in_range() macro which helps
to iterate over requested GPIO in a range. There are already
potential users of it, which are going to be converted
by the following patches.

For most of them for_each_requested_gpio() shortcut has been added.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200615150545.87964-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>