ARM: imx: mach-imx6ul: remove 14x14 EVK specific PHY fixup

Remove board specific PHY fixup introduced by commit:

| 709bc065 ("ARM: imx6ul: add fec MAC refrence clock and phy fixup init")

This fixup addresses boards with a specific configuration: a KSZ8081RNA
PHY with attached clock source to XI (Pin 8) of the PHY equal to 50MHz.

For the KSZ8081RND PHY, the meaning of the reg 0x1F bit 7 is different
(compared to the KSZ8081RNA). A set bit means:

- KSZ8081RNA: clock input to XI (Pin 8) is 50MHz for RMII
- KSZ8081RND: clock input to XI (Pin 8) is 25MHz for RMII

In other configurations, for example a KSZ8081RND PHY or a KSZ8081RNA
with 25Mhz clock source, the PHY will glitch and stay in not recoverable
state.

It is not possible to detect the clock source frequency of the PHY. And
it is not possible to automatically detect KSZ8081 PHY variant - both
have same PHY ID. It is not possible to overwrite the fixup
configuration by providing proper device tree description. The only way
is to remove this fixup.

If this patch breaks network functionality on your board, fix it by
adding PHY node with following properties:

	ethernet-phy@x {
		...
		micrel,led-mode = <1>;
		clocks = <&clks IMX6UL_CLK_ENET_REF>;
		clock-names = "rmii-ref";
		...
	};

The board which was referred in the initial patch is already fixed.
See: arch/arm/boot/dts/imx6ul-14x14-evk.dtsi

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>