arm64: dts: imx8mp: Drop EQoS clock workaround

The assigned-clock no longer have to be dropped, the clock are now
defined in clk-imx8mp.c and used by DWMAC driver to configure the
DWMAC clock. Drop the workarounds from U-Boot specific DT extras.

Signed-off-by: Marek Vasut <marex@denx.de>