The Pixel Pipeline (PXP) block is present on several i.MX SoCs
such as imx6dl, imx6sl, imx6ul, imx6sx, imx6ull and imx7d.

Select the PXP driver by default.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>