gpio: TODO: add delimiters between tasks for better readability

For better readability of the TODO, let's add some graphical delimiters
between tasks.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250321-gpio-todo-updates-v1-4-7b38f07110ee@linaro.org


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