MIPS: ingenic: rs90: Add dedicated VRAM memory region

Add a 1 MiB memory area dedicated to the video driver. This area will be
managed by Linux' CMA, so that the ingenic-drm driver can be sure to
always be able to allocate contiguous buffers.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/dts/ingenic/rs90.dts

@@ -16,6 +16,18 @@ memory {
 		reg = <0x0 0x2000000>;
 	};
 
+	reserved-memory {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		vmem: video-memory@1f00000 {
+			compatible = "shared-dma-pool";
+			reg = <0x1f00000 0x100000>;
+			reusable;
+		};
+	};
+
 	vcc: regulator {
 		compatible = "regulator-fixed";
 
@@ -300,6 +312,8 @@ &tcu {
 };
 
 &lcd {
+	memory-region = <&vmem>;
+
 	pinctrl-names = "default";
 	pinctrl-0 = <&pins_lcd>;
 };