I have the same device, same problem, but no solution yet. Here is my observation, hope it helps your investigation.
The device does not have RK805 PMU chip, it seems to be powered by some simple voltage regulators, unlike most other device (their dtb defined this PMU).
The eth0 when forced to 100Mbps mode and asign an IP address manually, use tcpdump listen on eth0, it can receive the ping package from other machine, but cannot send respond, so it appears to be ping failed to reach this Box. Likely the TX part of this device is not configured properly somehow.
There might be some pinctrl driver issue (not sure) related with GMAC pins, patches is floating around on kernel mail list, not sure how it will impact this device.
