xtensa: configure shared DMA pool reservation in kc705 DTS

Add example 64MByte long reservation in the first 512MBytes of physical
memory used as shared DMA pool.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/boot/dts/kc705.dts

@@ -11,4 +11,20 @@ memory@0 {
 		device_type = "memory";
 		reg = <0x00000000 0x38000000>;
 	};
+
+	reserved-memory {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		/* global autoconfigured region for contiguous allocations */
+		linux,cma {
+			compatible = "shared-dma-pool";
+			reusable;
+			size = <0x04000000>;
+			alignment = <0x2000>;
+			alloc-ranges = <0x00000000 0x20000000>;
+			linux,cma-default;
+		};
+	};
 };