rockchip: add px30 architecture core

Add core architecture code to support the px30 soc.
This includes a separate tpl board file due to very limited
sram size as well as a non-dm sdram driver, as this also has
to fit into the tiny sram.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>