gpio: deprecate devm_gpiod_unhinge()

gpio: deprecate devm_gpiod_unhinge()

This function was introduced as a workaround for an issue with resource
ownership in the regulator subsystem. Rather than passing the ownership
of a GPIO, we should make the regulator core be able to deal with
resources it didn't request. Deprecate this function so that we don't
get more users in the tree.

Link: https://lore.kernel.org/r/20250401-gpio-todo-remove-nonexclusive-v2-2-7c1380797b0d@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>