arm64: dts: amlogic: meson-g12: use the G12A specific dwmac compatible

We have a dedicated "amlogic,meson-g12a-dwmac" compatible string for the
Ethernet controller since commit 3efdb924 ("dt-bindings: net:
dwmac-meson: Add a compatible string for G12A onwards").
Using the AXG compatible string worked fine so far because the
dwmac-meson8b driver doesn't handle the newly introduced register bits
for G12A. However, once that changes the driver must be probed with the
correct compatible string to manage these new register bits.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200925211743.537496-1-martin.blumenstingl@googlemail.com