arm64: dts: imx8mm-verdin: update iomux configuration

Update IOMUX configuration as required by the hardware design team.
Signed-off-by: NAndrejs Cainikovs <andrejs.cainikovs@toradex.com>
Signed-off-by: NMarcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>