The PCI Express x1 and x4 IP Core is supported by both SC and ECP2 device families. The minimal ECP2M device needed to support the core is LFE2M-20E-6F484C, and the minimal SC device needed is LFSC3GA15E-6F900C.
Newer Lattice FPGA families that supported PCIe IP are CrossLink-NX, Certus-NX, CertusPro-NX, MachXO5T-NX, Avant-G, Avant-X.
Refer below link for their respective Demo Designs and User Guides.
https://www.latticesemi.com/products/designsoftwareandip/intellectualproperty/ipcore/ipcores05/pci-express-x1-x4-ip-core