rockchip: arm64: rk3399: syscon addition for rk3399

rk3399 has different syscon registers which may used in spl,
add to support rk3399 spl.

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>