dt-bindings: net: meson-dwmac: new compatible name for AXG SoC

We need to introduce a new compatible name for the Meson-AXG SoC
in order to support the RMII 100M ethernet PHY, since the PRG_ETH0
register of the dwmac glue layer is changed from previous old SoC.

Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>