dt-bindings: fpga: add compatible value to Stratix10 SoC FPGA manager binding

Add a compatible property value to Stratix10 SoC FPGA manager binding file

Signed-off-by: Richard Gong <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Moritz Fischer <[e-mail]>

Documentation/devicetree/bindings/fpga/intel-stratix10-soc-fpga-mgr.txt

···
 The fpga_mgr node has the following mandatory property, must be located under
 firmware/svc node.
 
-- compatible : should contain "intel,stratix10-soc-fpga-mgr"
+- compatible : should contain "intel,stratix10-soc-fpga-mgr" or
+	       "intel,agilex-soc-fpga-mgr"
 
 Example: