arm64: dts: colibri-imx8x: move pinctrl property from SoM to eval board

Each carrier board device tree except the eval board one already override
iomuxc pinctrl property to configure unused pins as gpio.
So move also the pinctrl property to eval board device tree.
Leave the pin group definition in imx8x-colibri.dtsi to avoid duplication
and simplify configuration of gpio.

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Andrejs Cainikovs <andrejs.cainikovs@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>