ARM: dts: aspeed: witherspoon: Enable XDMA engine

Add a reserved memory node for the VGA memory. Add the XDMA engine node,
enable it, and point it's memory region to the VGA memory.

Signed-off-by: Eddie James <[e-mail]>
Signed-off-by: Joel Stanley <[e-mail]>

arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts

···
 			reg = <0x98000000 0x04000000>; /* 64M */
 		};
 
+		vga_memory: region@9f000000 {
+			no-map;
+			compatible = "shared-dma-pool";
+			reg = <0x9f000000 0x01000000>; /* 16M */
+		};
+
 		gfx_memory: framebuffer {
 			size = <0x01000000>;
 			alignment = <0x01000000>;
···
 &video {
 	status = "okay";
 	memory-region = <&video_engine_memory>;
+};
+
+&xdma {
+	status = "okay";
+	memory-region = <&vga_memory>;
 };
 
 #include "ibm-power9-dual.dtsi"