ipq40xx: dts: add ethernet0 alias for all devices

ipq40xx: dts: add ethernet0 alias for all devices

Updating the driver patches for ipq40xx (correctly) removed the
ethernet0 alias from qcom-ipq4019.dtsi; however, on some devices this
alias is needed for the bootloader to set MAC addresses in the FDT.

As it is unknown which devices actually need the alias, simply add it to
all devices trees for now that enable the &gmac now to avoid regressions
from previous OpenWrt releases. The additional alias should not cause any
issues even when it is not needed.

A TODO comment is added to the same Device Trees to document that the
alias may not be needed (hopefully preventing it from being copied
unnecessarily to newly added devices in the future). The following
devices are known to need the alias for correct MAC address assignment,
so no TODO comment is added:

- FRITZ!Box 4040
- FRITZ!Box 7530

Fixes: cd9c7211241e ("ipq40xx: 6.1: use latest DSA and ethernet patches")
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Link: https://github.com/openwrt/openwrt/pull/17442
Signed-off-by: Robert Marko <robimarko@gmail.com>