ARM: dts: imx6sx: Complete the PXP support

According to Documentation/devicetree/bindings/media/fsl-pxp.txt,
only one PXP clock needs to be described and it should be named
"axi".

Also pass the compatible string as suggested in the bindings doc.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6sx.dtsi

@@ -1194,11 +1194,11 @@ csi1: csi@2214000 {
 				};
 
 				pxp: pxp@2218000 {
+					compatible = "fsl,imx6sx-pxp", "fsl,imx6ull-pxp";
 					reg = <0x02218000 0x4000>;
 					interrupts = <GIC_SPI 8 IRQ_TYPE_LEVEL_HIGH>;
-					clocks = <&clks IMX6SX_CLK_PXP_AXI>,
-						 <&clks IMX6SX_CLK_DISPLAY_AXI>;
-					clock-names = "pxp-axi", "disp-axi";
+					clocks = <&clks IMX6SX_CLK_PXP_AXI>;
+					clock-names = "axi";
 					status = "disabled";
 				};