Input: gpio_keys - scan gpio state at probe and resume time

We need to read and report gpio state when we bind the driver to the
device and upon resume so that userspace has correct state of the
switches (and keys but they are less important since, even if they
are happened to be pressed, we'd expect them to be released fairly
soon).

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>