mediatek: update LED/Key bindings for Buffalo WSR-2533DHP2

mediatek: update LED/Key bindings for Buffalo WSR-2533DHP2

Update LED and key nodes with newer DeviceTree bindings for WSR-2533DHP2.

- LED
  - use led-[0-9] for node name of LEDs
  - add "color" and "function" properties
  - drop default-state = "on" from green:power LED
    - this LED will be turned on by led-running alias

- key
  - drop unnecessary poll-interval property
  - use key-[0-9] for node name of keys

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
(cherry picked from commit 6b8e7144c8863686a8ddef6f4fcebb3b8cf85f36)