dt-bindings: fpga: Add binding doc for versal fpga manager

This patch adds binding doc for versal fpga manager driver.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: Appana Durga Kedareswara rao <appana.durga.rao@xilinx.com>
Link: https://lore.kernel.org/r/20210626155248.5004-3-nava.manne@xilinx.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>