Per nxp,dwmac-imx.yaml, phy-supply is not a valid property.

Remove it to fix the following dt-schema warning:

imx93-var-som-symphony.dtb: ethernet@428a0000: Unevaluated properties are not allowed ('phy-supply' was unexpected)
	from schema $id: http://devicetree.org/schemas/net/nxp,dwmac-imx.yaml#

The reg_eqos_phy regulator is marked as 'regulator-always-on', so it is
safe to remove the phy-supply property.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>