dt-bindings: fsl: add compatible for imx7ulp evk

Add compatible string for imx7ulp evk board.

Cc: devicetree@vger.kernel.org
Cc: Shawn Guo <shawnguo@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/arm/fsl.txt

@@ -101,6 +101,10 @@ i.MX7 SabreSD Board
 Required root node properties:
     - compatible = "fsl,imx7d-sdb", "fsl,imx7d";
 
+i.MX7ULP Evaluation Kit
+Required root node properties:
+    - compatible = "fsl,imx7ulp-evk", "fsl,imx7ulp";
+
 Generic i.MX boards
 -------------------
 
@@ -123,6 +127,10 @@ i.MX6q generic board
 Required root node properties:
     - compatible = "fsl,imx6q";
 
+i.MX7ULP generic board
+Required root node properties:
+    - compatible = "fsl,imx7ulp";
+
 Freescale Vybrid Platform Device Tree Bindings
 ----------------------------------------------