oak: Add LED control for rev3
oak: Add LED control for rev3

Oak rev3 has 2 dual-color LEDs to indicate the AP power & battery
status. The behavior has been redefined and distinguish from rev2
by board version API.

BRANCH=none
BUG=none
TEST=manual
1. define CONFIG_BOARD_OAK_REV_2 in board.h
   make -j BOARD=oak
2. define CONFIG_BOARD_OAK_REV_3 in board.h
   make -j BOARD=oak
both cases should be built successfully.
And Check the PWR & BAT LED.

Change-Id: Ic60d6f91002c3534e4c12a27e5c89bc2d0a1ecfd
Signed-off-by: Ben Lok <310171a828df105188e0b545d65d6370e8133283@mediatek.com>
Reviewed-on: https://chromium-review.googlesource.com/290061
Reviewed-by: Rong Chang <3a05493f7adfb36d203f663b3bc2ba30e9d6284f@chromium.org>

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