gpio: 104-dio-48e: Implement struct dio48e_gpio

A private data structure struct dio48e_gpio is introduced to facilitate
passage of the regmap and IRQ mask state for the device to the callback
dio48e_handle_mask_sync(). This is in preparation for the removal of the
handle_mask_sync() map parameter in a subsequent patch.

Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/ca710d14a710fee44f7911f2a84b6a55570561ee.1679323449.git.william.gray@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>