ARM: dts: imx7-colibri: fix 1.8V/UHS support

Add pinmuxing and do not specify voltage restrictions for the usdhc
instance available on the modules edge connector. This allows to use
SD-cards with higher transfer modes if supported by the carrier board.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>