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.comSigned-off-by: NBharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NRob Herring <robh@kernel.org>