net: ethernet: stmmac: dwmac-rk: Add gmac support for rk3588

Add constants and callback functions for the dwmac on RK3588 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>
[rebase, squash fixes]
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>