ram: rockchip: add common code for sdram driver

There are some function like os_reg setting, capacity detect functions,
can be used as common code for different Rockchip SoCs, add a
sdram_common.c for all these functions.

Signed-off-by: YouMin Chen <cym@rock-chips.com>
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
4 files changed