gpio: deprecate the GPIOD_FLAGS_BIT_NONEXCLUSIVE flag

The non-exclusive GPIO request flag looks like a functional feature but
is in fact a workaround for a corner-case that got out of hand. It should
be removed so deprecate it officially so that nobody uses it anymore.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250401-gpio-todo-remove-nonexclusive-v2-1-7c1380797b0d@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>