dt-bindings: reset: Add bindings for ZynqMP reset driver

Add documentation to describe Xilinx ZynqMP reset driver
bindings.

Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Signed-off-by: Jolly Shah <jollys@xilinx.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>