ath79: convert devices to interrupt-driven gpio-keys

ath79: convert devices to interrupt-driven gpio-keys

This converts all remaining devices to use interrupt-driven
gpio-keys compatible instead of gpio-keys-polled.
The poll-interval is removed.

Only ar7240_netgear_wnr612-v2 is kept at gpio-keys-polled, as
this one is using ath9k keys.

Signed-off-by: Adrian Schmutzler <[email protected]>
Tested-by: Karl Palsson <[email protected]>
Tested-by: Dmitry Tunin <[email protected]>