ARM: dts: imx6qdl: use enet_clk_ref instead of enet_out for the FEC node

Old imx6q machine code makes RGMII/RMII clock direction decision based on
configuration of "ptp" clock. "enet_out" is not used and make no real
sense, since we can't configure it as output or use it as clock
provider.

Instead of "enet_out" use "enet_clk_ref" which is actual selector to
choose between internal and external clock source:

FEC MAC <---------- enet_clk_ref <--------- SoC PLL
                         \
			  ^------<-> refclock PAD (bi directional)
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl.dtsi

@@ -1049,8 +1049,8 @@ fec: ethernet@2188000 {
 				clocks = <&clks IMX6QDL_CLK_ENET>,
 					 <&clks IMX6QDL_CLK_ENET>,
 					 <&clks IMX6QDL_CLK_ENET_REF>,
-					 <&clks IMX6QDL_CLK_ENET_REF>;
-				clock-names = "ipg", "ahb", "ptp", "enet_out";
+					 <&clks IMX6QDL_CLK_ENET_REF_SEL>;
+				clock-names = "ipg", "ahb", "ptp", "enet_clk_ref";
 				fsl,stop-mode = <&gpr 0x34 27>;
 				nvmem-cells = <&fec_mac_addr>;
 				nvmem-cell-names = "mac-address";