That's right, our patches can only be re-used in the versions they were rebased on. Since the 2020.1 branch contains important patches related to the DDR4 initialization, I would upgrade to that version.
If you insist on 2019.1, you can try back-porting the 2020.1 embeddedsw commits. We were forced to expand the approved DDR modules we ship the Genesys ZU with and those can only be supported with the DDR4 init patches.
