Hi Roby,
i.MX8MM EVK board use AR8031 as Ethernet PHY, but I see it's KSZ9031 in your log. So you don't use iMX official EVK board, right? if yes, you need to check your device tree. In addition, you need to check enable-Xenomai-driver.config in release package of xenomai-arm64, if you apply the config for you kernel config.