dt-bindings: fpga: add binding doc for microchip-spi fpga mgr

Add Device Tree Binding doc for Microchip Polarfire FPGA Manager using
slave SPI to load .dat formatted bitstream image.

Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20220623163248.3672-5-i.bornyakov@metrotek.ru
Signed-off-by: Xu Yilun <yilun.xu@intel.com>

Documentation/devicetree/bindings/fpga/microchip,mpf-spi-fpga-mgr.yaml

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/fpga/microchip,mpf-spi-fpga-mgr.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Microchip Polarfire FPGA manager.
+
+maintainers:
+  - Ivan Bornyakov <i.bornyakov@metrotek.ru>
+
+description:
+  Device Tree Bindings for Microchip Polarfire FPGA Manager using slave SPI to
+  load the bitstream in .dat format.
+
+properties:
+  compatible:
+    enum:
+      - microchip,mpf-spi-fpga-mgr
+
+  reg:
+    description: SPI chip select
+    maxItems: 1
+
+  spi-max-frequency: true
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            fpga_mgr@0 {
+                    compatible = "microchip,mpf-spi-fpga-mgr";
+                    spi-max-frequency = <20000000>;
+                    reg = <0>;
+            };
+    };