imx6qdl-wandboard can be connected to a OV5645 camera via
MIPI CSI port. Add support for it.

PAD_GPIO_6 has been originally used for the Ethernet FEC
ERR006687 workaround, but it needs to be used to provide the
camera sensor clock, so adjust it accordingly.
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>