Is the ZSBL of freedom 32-bit or 64-bit

Hi,
We have developed a new board based on VCU118. The FPGA model is the same as that of VCU118, but our memory controller is dual-channel, that is, there are two memory modules on the board, each of which supports up to 8 GB. Then, can I directly access the 16 GB DDR4 memory space in the ZSBL phase?
Thank you very much!