board: move all the rockchip board in one folder

board: move all the rockchip board in one folder

The 'evb_rk3036' and 'kylin' is not a vendor name, let's replace them
to 'rockchip' which is a real _vendor_ name, and meet the architecure
'board/<vendor>/<board-name>/'.

More boards from rockchip like evb_rk3288, evb_rk3399 will comes later.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Eddie Cai <eddie.cai.kernel@gmail.com>