Documentation: gpio: documentation for optional getters functions
Documentation: gpio: documentation for optional getters functions

Add a mention about the _optional variants of (devm_)gpiod_get*().

Signed-off-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@nvidia.com>
Signed-off-by: Linus Walleij <9cd9d802d23c0ed5e224beabf4ae4a5c478746ef@linaro.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs