gpio: aggregator: add possibility to attach data to the forwarder

gpio: aggregator: add possibility to attach data to the forwarder

Add a data pointer to store private data in the forwarder.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://lore.kernel.org/r/20250811-aaeon-up-board-pinctrl-support-v9-8-29f0cbbdfb30@bootlin.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>