ARM: dts: artpec: migrate ethernet to stmmac binding

The snps,dwc-qos-ethernet binding is still supported as a glue layer
in the stmmac driver.
However, since the snps,dwc-qos-ethernet binding is now deprecated,
migrate to stmmac's native binding.

At the same time, enable features supported by the stmmac driver,
such as PTP, LPI, and an additional tx queue.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>