Documentation: gpio: Add a compatibility and feature list for PCA953x

Documentation: gpio: Add a compatibility and feature list for PCA953x

I went through all the datasheets and created this note listing
chip functions and register layouts.

Signed-off-by: Levente Révész <levente.revesz@eilabs.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20251112224924.2091880-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>