arm: mvebu: clearfog: support 512MB memory size from tlv eeprom

Handle 2GBit memory size value "2" from tlv eeprom on ddr
initialisation, to support SoMs with 512MB ddr memory.

Signed-off-by: Josua Mayer <josua@solid-run.com>
Reviewed-by: Stefan Roese <sr@denx.de>