ARM: dts: imx7-colibri: mux pull-ups where appropriate

Use pull-ups instead of pull-downs for the pins which are already
pulled-up externally.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>