ARM: dts: imx6sx-sdb-reva: Add revision in board compatible string

i.MX6SX SDB Rev-A board should use its own board compatible
string instead of default i.MX6SX SDB board.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sx-sdb-reva.dts

@@ -6,6 +6,7 @@
 
 / {
 	model = "Freescale i.MX6 SoloX SDB RevA Board";
+	compatible = "fsl,imx6sx-sdb-reva", "fsl,imx6sx";
 };
 
 &i2c1 {