PCI: xilinx-cpm: Add YAML schemas for Versal CPM Root Port

Add YAML schemas documentation for Versal CPM Root Port driver.

Link: https://lore.kernel.org/r/1592312214-9347-2-git-send-email-bharat.kumar.gogada@xilinx.com
Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>