rockchip: rk3328: add soc basic support

RK3328 is a SoC from Rockchip with quad-core Cortex-A53 CPU.
It supports two USB2.0 EHCI ports. Other interfaces are very
much like RK3288, the DRAM are 32bit width address and support
address from 0 to 4GB-16MB range.

Signed-off-by: William Zhang <william.zhang@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
Add empty arch/arm/mach-rockchip/rk3328/Kconfig to avoid build error:
Signed-off-by: Simon Glass <sjg@chromium.org>