arm64: dts: imx8dxl-ss-conn: Move conn_enet0_root_clk outside of soc

The conn_enet0_root_clk node does not have any register associated with it,
so it should be moved outside of soc to fix schema warning from
simple-bus.yaml.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>