dt-bindings: fpga: Add compatible value for Xilinx DFX AXI shutdown manager

This patch Adds compatible value for Xilinx Dynamic Function eXchnage(DFX)
AXI Shutdown manager IP.

Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Reviewed-by: Tom Rix <trix@redhat.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>