media: dt-bindings: media: fsl-pxp: add missing imx6sll

i.MX6SLL also has a pxp, so mention it among others in the bindings doc.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/media/fsl-pxp.txt

@@ -8,7 +8,7 @@ i.MX SoCs from i.MX23 to i.MX7.
 
 Required properties:
 - compatible: should be "fsl,<soc>-pxp", where SoC can be one of imx23, imx28,
-  imx6dl, imx6sl, imx6ul, imx6sx, imx6ull, or imx7d.
+  imx6dl, imx6sl, imx6sll, imx6ul, imx6sx, imx6ull, or imx7d.
 - reg: the register base and size for the device registers
 - interrupts: the PXP interrupt, two interrupts for imx6ull and imx7d.
 - clock-names: should be "axi"