rockchip: sdram: extend to use sys_reg3 for capacity info

rockchip: sdram: extend to use sys_reg3 for capacity info

Since we have new DRAM type and to support different DRAM size in different
CS, we need more bits, so introduce sys_reg3 to record the info.
Note that the info in sys_reg3 is extension to sys_reg2 and the info in
sys_reg2 is the same as before. We define the DRAM_INFO with sys_reg3 as
VERSION2.
All the ENC macro are moved to sdram_common.h since the sdram.c only
need to do the info decode.

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