gpio: regmap: Allow to provide init_valid_mask callback

gpio: regmap: Allow to provide init_valid_mask callback

Allows to populate the gpio_regmap_config structure with
init_valid_mask() callback to set on the final gpio_chip structure.

Reviewed-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Link: https://lore.kernel.org/r/20250824-mdb-max7360-support-v14-6-435cfda2b1ea@bootlin.com
Signed-off-by: Lee Jones <lee@kernel.org>