rockchip: dts: rk3399: update for spl require driver

Add syscon and dmc node, and 'u-boot,dm-pre-reloc' option for
required driver.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Added rockchip tag:
Signed-off-by: Simon Glass <sjg@chromium.org>