ath79: change WPS to Wifi button on TL-WPA8630P v2

ath79: change WPS to Wifi button on TL-WPA8630P v2

Both TL-WPA8630(P) v1 and v2 feature a button labelled "WiFi".
While this is implemented as KEY_RFKILL for v1 in ar71xx and ath79,
the v2 sets it up as WPS button.

According to the manual, the behavior in OEM firmware is:
"Press and hold the button for 1 second to copy wireless settings
from the main router to the extender. Go to Wi-Fi Clone for more
information. Press and hold the button for at least 5 seconds to
turn the wireless function on or off."

Consequently, and since this is historic behavior on v1 in OpenWrt,
we set this button to KEY_RFKILL on both revisions.

Fixes: ab74def0db93 ("ath79: add support for TP-Link TL-WPA8630P v2")
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>