rockchip: mkimage: add support for px30

Add the table entry for px30 socs.
The px30 has 10K of sram available.

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