ARM: dts: imx: imx8qm-rom7720: Fix AR8031 phy-mode

ARM: dts: imx: imx8qm-rom7720: Fix AR8031 phy-mode

Fixed wrong PHY Interface Mode

    As per kernel commit 0672d22a1924 ("ARM: dts: imx: Fix the AR803X phy-mode)
    the correct phy-mode should be "rgmii-id", so fix it accordingly
    to fix the Ethernet regression.

    This problem has been exposed by commit:

    commit 13114f38e2ccea9386726d8b9831dfc310589548

    Fix the phy-mode accordingly to fix the regression.

Signed-off-by: Oliver Graute <oliver.graute@kococonnector.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Vladimir Oltean <vladimir.oltean@nxp.com>