The ZCU102 board supports PCIe Gen2 x1 by default, however x2 and x4 should be possible by modifying some settings in Vivado (for the FSBL), and correctly setting the external GTR switch (see page 86 of the user guide).
For Linux, the GTR switch setting at boot time can be controlled in the device tree. The device tree also needs modifying to remove the DP/SATA/USB3 devices if these are disabled so the PCIe can use their GTR lanes.