The existing gpio-keys driver can be usable only for GPIO lines with
interrupt support. Several devices have buttons connected to a GPIO
line which is not capable to generate interrupts. This patch adds a
new input driver using the generic GPIO layer and the input-polldev
to support such buttons.

[Ben Gardiner <bengardiner@nanometrics.ca: fold code to use more
 of the original gpio_keys infrastructure; cleanups and other
 improvements.]
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Signed-off-by: NBen Gardiner <bengardiner@nanometrics.ca>
Tested-by: NBen Gardiner <bengardiner@nanometrics.ca>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>