net: stmmac: dwmac-rk: Add RK3128 GMAC support

Add constants and callback functions for the dwmac on rk3128 soc.
As can be seen, the base structure is the same, only registers
and the bits in them moved slightly.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/rockchip-dwmac.txt

@@ -4,6 +4,7 @@ The device node has following properties.
 
 Required properties:
  - compatible: should be "rockchip,<name>-gamc"
+   "rockchip,rk3128-gmac": found on RK312x SoCs
    "rockchip,rk3228-gmac": found on RK322x SoCs
    "rockchip,rk3288-gmac": found on RK3288 SoCs
    "rockchip,rk3328-gmac": found on RK3328 SoCs