ARM: dts: imx: imx6qdl.dtsi: add mipi_csi tag

We will reference mipi_csi from board
dts files.
Signed-off-by: NTroy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx6qdl.dtsi

@@ -839,7 +839,7 @@
 				status = "disabled";
 			};
 
-			mipi@021dc000 { /* MIPI-CSI */
+			mipi_csi: mipi@021dc000 {
 				reg = <0x021dc000 0x4000>;
 			};