gpiolib: introduce devm_fwnode_gpiod_get_optional() wrapper

gpiolib: introduce devm_fwnode_gpiod_get_optional() wrapper

The helper makes it easier to handle optional GPIOs and simplifies the
error handling code.

Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/20260126-gpio-devm_fwnode_gpiod_get_optional-v2-1-ec34f8e35077@pengutronix.de
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>