As per i.MX 8M Reference Manual section 18.104.22.168, it says up to 8GB memory capacity.
So we assumed 8GB should not be a issue. Can you please reconfirm if 8GB LPDDR4 is not supported.
Section 22.214.171.124 concerns parameters of the DRAM controller as SNPS IP (taken separately by itself).
Restriction relates to address space, available for DRAM, in the i.MX8M SOC.