spi: dt-bindings: axi-spi-engine: add SPI offload properties

The AXI SPI Engine has support for hardware offloading capabilities.
This includes a connection to a DMA controller for streaming RX or TX
data and a trigger input for starting execution of the SPI message
programmed in the offload. It is designed to support up to 32 offload
instances.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250207-dlech-mainline-spi-engine-offload-2-v8-6-e48a489be48c@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/adi,axi-spi-engine.yaml

@@ -41,6 +41,26 @@ properties:
       - const: s_axi_aclk
       - const: spi_clk
 
+  trigger-sources:
+    description:
+      An array of trigger source phandles for offload instances. The index in
+      the array corresponds to the offload instance number.
+    minItems: 1
+    maxItems: 32
+
+  dmas:
+    description:
+      DMA channels connected to the input or output stream interface of an
+      offload instance.
+    minItems: 1
+    maxItems: 32
+
+  dma-names:
+    items:
+      pattern: "^offload(?:[12]?[0-9]|3[01])-[tr]x$"
+    minItems: 1
+    maxItems: 32
+
 required:
   - compatible
   - reg
@@ -59,6 +79,10 @@ examples:
         clocks = <&clkc 15>, <&clkc 15>;
         clock-names = "s_axi_aclk", "spi_clk";
 
+        trigger-sources = <&trigger_clock>;
+        dmas = <&dma 0>;
+        dma-names = "offload0-rx";
+
         #address-cells = <1>;
         #size-cells = <0>;