Input: adp5588-keys - add support for pure gpio

Keypad specific setup is relaxed if no keypad rows/columns are specified,
enabling a purely gpio operation.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Utsav Agarwal <utsav.agarwal@analog.com>
Link: https://lore.kernel.org/r/20240826-adp5588_gpio_support-v11-2-3e5ac2bd31b7@analog.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>