ARM: dts: net: dwc_eth_qos: Fix i.MX8MP compatible string

ARM: dts: net: dwc_eth_qos: Fix i.MX8MP compatible string

The correct compatible string for i.MX8MP variant of DWC EQoS MAC
is "nxp,imx8mp-dwmac-eqos", use it. Drop the two current users of
the current wrong compatible string to avoid breaking them.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>