I can't get the Board Definitions link to work at all. However, there is a copy of it here:
That is an archive that contains all the MicroZeds and PicoZed versions, but you will see 4 folders with picozed_70xx_fmc1 which is for the PicoZed SOM plugged into the PicoZed FMC Carrier Card V1. Even though it is labeled through 2017.4, I think it will also work for 2018.x and 2019.x.
The PicoZed FMC V1 Reference Design page also contains older PetaLinux BSPs. Looks like the most recent ones were 2016.2.