colibri-imx8qxp: rename all occurences to colibri-imx8x

The Toradex product is called colibri-imx8x consisting of SoM with
i.MX8QXP and i.MX8DX SoCs.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@toradex.com>
diff --git a/doc/board/toradex/colibri-imx8x.rst b/doc/board/toradex/colibri-imx8x.rst
index 244e5a4..616f40a 100644
--- a/doc/board/toradex/colibri-imx8x.rst
+++ b/doc/board/toradex/colibri-imx8x.rst
@@ -52,7 +52,7 @@
 
 .. code-block:: bash
 
-   $ make colibri-imx8qxp_defconfig
+   $ make colibri-imx8x_defconfig
    $ make u-boot-dtb.imx
 
 Load the U-Boot Binary Using UUU