mvebu - switch to orion-timer

Hello Stefan! Now when U-Boot contains new orion-timer.c driver, which Michael wrote, I think that it mvebu platform should switch to use it. Because build process for armada boards prints deprecation warning that new timer is not being used. Could you look at it, if it is possible to do global switch for mach-mvebu and mach-kirkwood? I think it does not make sense to do per-board switching as it is de-facto platform related code.