gpio: mvebu: Make use of for_each_requested_gpio()

Make use of for_each_requested_gpio() instead of home grown analogue.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200615150545.87964-4-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>