rockchip: SPL: fix ordering of DRAM init

The common SPL code reordered the DRAM initialization before
rockchip_stimer_init(), which as far as I can tell causes the RK3399 to
lock up completely.

Fix this issue in the common code by putting the DRAM init back after
timer init. I have only tested this on the RK3399, but it wouldn't make
any sense for the timer init to require DRAM be set up on any system.

Fixes: b7abef2e ("rockchip: rk3399: Migrate to use common spl board file")

Signed-off-by: Thomas Hebb <tommyhebb@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>