GXM "no phy at addr -1" Ethernet error

[chewitt]

Some users testing with GXB device-tree files report no Ethernet, and when logs can be retrieved the following is seen:

Dec 20 18:15:51.776445 LibreELEC kernel: meson8b-dwmac c9410000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
Dec 20 18:15:51.778860 LibreELEC kernel: meson8b-dwmac c9410000.ethernet eth0: no phy at addr -1
Dec 20 18:15:51.782522 LibreELEC kernel: meson8b-dwmac c9410000.ethernet eth0: __stmmac_open: Cannot attach to PHY (error: -19)

The issue was not reported on kernels before 6.1, but it's not necessarily correlating to a regression with the 6.1.x kernel release as AMGLX was not in widespread use before LE11b1 which shipped with 6.1.x kernel.