dts:imx6qdl-santvend: Set default CMA to 256 MiB

Double the default CMA allocation amount to 256 MiB only for Santvend devices.

arch/arm/boot/dts/seconorth/imx6qdl-santvend.dtsi

@@ -19,6 +19,12 @@ aliases {
 		serial4 = &uart1;	/* GSM */
 	};
 
+	reserved-memory {
+		linux,cma {
+			size = <0x10000000>; /* 256 MiB */
+		};
+	};
+
 	backlight2: backlight@1 {
 		compatible = "pwm-backlight";
 		pwms = <&pwm2 0 50000 0>;