ARM: dts: colibri-imx6ull: fix snvs pinmux group

A pin controlled by the iomuxc-snvs pin controller must be
specified under the dtb's iomuxc-snvs node.

Move the one and only pin of that category from the iomuxc node
and set the pinctrl-0 using it accordingly.

Fixes: 2aa9d620 ("ARM: dts: imx6ull-colibri: add touchscreen device nodes")
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>