Linux has built-in support for runtime PM and Xilinx provides the required drivers to make this work on Zynq UltraScale+ devices. Refer to this page for a detailed tutorial on Linux PM: https://xilinx-wiki.atlassian.net/wiki/spaces/A/pages/18842232 .
CPU specific power management techniques are discussed in more details on this page: https://xilinx-wiki.atlassian.net/wiki/spaces/A/pages/1417117726 .