arm64: dts: imx93: add fsl,stop-mode property to support WOL

Add fsl,stop-mode property for FEC to support Wake-on-LAN (WOL)
feature. Otherwise, the WOL feature of FEC does not work.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>