mvebu: update and refactor uDPU DTS

mvebu: update and refactor uDPU DTS

uDPU DTS has pending upstream fixups, so backport those as well as split
the DTS into a DTSI and DTS in preparation for euroDPU support which
uses uDPU as the base.

Ethernet aliases have not yet been sent upstream but will be soon in order
for U-boot to set the correct MAC on both ethernet interfaces instead of
just one.

Since U-boot environment now has its own partition, update the envtools
config script to search for it instead.

Patch hardcoding PHY mode is also not applicable anymore, so drop it and
set in the uDPU DTS directly.

Signed-off-by: Robert Marko <robert.marko@sartura.hr>