ram: starfive: Read memory size information from EEPROM

StarFive VisionFive 2 has two versions, 1.2A and 1.3B, each version of
DDR capacity includes 2G/4G/8G, a DT can not support multiple
capacities, so the capacity size information is recorded to EEPROM, when
DDR initialization required capacity size information is read from
EEPROM.

If there is no information in EEPROM, it is initialized with the default
size defined in DT.

Signed-off-by: Yanhong Wang <yanhong.wang@starfivetech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>