db410c: add reserved-memory node to dts

If lk lights up display and populates simple-framebuffer node, it will
also setup a reserved-memory node (needed by simplefb on linux).  But
it isn't clever enough to cope when the reserved-memory node is not
present.

Signed-off-by: Rob Clark <robdclark@gmail.com>

arch/arm/dts/dragonboard410c.dts

@@ -23,11 +23,16 @@
 		reg = <0 0x80000000 0 0x3da00000>;
 	};
 
+	reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+	};
+
 	chosen {
 		stdout-path = "/soc/serial@78b0000";
 	};
 
-
 	soc {
 		#address-cells = <0x1>;
 		#size-cells = <0x1>;