rockchip: rk3036: change ddr frequency to 400M

emac may use dpll as clock parent, and it request the clock frequency
multiples of 50, so change ddr frequency to 400M.

Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>