arm64: dts: imx8mp: add eqos node and alias

Add EQOS GMAC node per Documentation/devicetree/bindings/net/imx-dwmac.txt ,
leave out the nvmem entries as that is not yet available, so the MAC has to
be passed in via DT by the bootloader.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dong Aisheng <aisheng.dong@nxp.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Teresa Remmet <t.remmet@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>