ARM: spitz: Use software nodes/properties for the GPIO-driven buttons

Convert the Spitz to use software nodes and static properties to
describe GPIOs for the GPIO-driven buttons.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240805014710.1961677-4-dmitry.torokhov@gmail.com


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