dt-bindings: fec: Make the phy-reset-gpio polarity explicit

The GPIO polarity passed to phy-reset-gpio is ignored by the FEC
driver and it is assumed to be active low.

It can be active high only when the 'phy-reset-active-high' property
is present.

The current examples pass active high polarity and work fine, but
in order to improve the documentation make it explicit what the real
polarity is.

Signed-off-by: Fabio Estevam <[e-mail]>
Acked-by: Fugang Duan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/fsl-fec.txt

···
 	reg = <0x83fec000 0x4000>;
 	interrupts = <87>;
 	phy-mode = "mii";
-	phy-reset-gpios = <&gpio2 14 0>; /* GPIO2_14 */
+	phy-reset-gpios = <&gpio2 14 GPIO_ACTIVE_LOW>; /* GPIO2_14 */
 	local-mac-address = [00 04 9F 01 1B B9];
 	phy-supply = <&reg_fec_supply>;
 };
···
 	reg = <0x83fec000 0x4000>;
 	interrupts = <87>;
 	phy-mode = "mii";
-	phy-reset-gpios = <&gpio2 14 0>; /* GPIO2_14 */
+	phy-reset-gpios = <&gpio2 14 GPIO_ACTIVE_LOW>; /* GPIO2_14 */
 	local-mac-address = [00 04 9F 01 1B B9];
 	phy-supply = <&reg_fec_supply>;
 	phy-handle = <&ethphy>;