imx8mp_evk: Simplify Ethernet initialization

imx8mp_evk: Simplify Ethernet initialization

With DM enabled, there is no need for board code to initialize
the Ethernet interfaces.

The RTL8211FDI Ethernet PHYs have 25MHz oscillator, so there is no
need to enable the RGMII TX clk output.

Also, there is no need for describing the deprecated phy-reset FEC
properties, nor passing reset properties to the EQOS interface in
u-boot.dtsi.

Remove all these unneeded pieces.

Tested both Ethernet interfaces after these changes.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>