Input: adp5588-keys - add regulator support

Support feeding VCC through a regulator.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220829131553.690063-10-nuno.sa@analog.com


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