Per nxp,dwmac-imx.yaml, it is not valid to pass 'phy-supply'.

Remove it to fix the following dt-schema warning:

ethernet@30bf0000: Unevaluated properties are not allowed ('phy-supply' was unexpected)
	from schema $id: http://devicetree.org/schemas/net/nxp,dwmac-imx.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Tested-by: Umang Jain <umang.jain@ideasonboard.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>