imx9: Calculate DDR size from DDRC setting

To avoid using static setting for ECC enabled DDR size, switch
to calculate DDR size from DDRC setting

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>