net: gmac_rockchip: Add rk3328 gmac support

net: gmac_rockchip: Add rk3328 gmac support

The GMAC2IO in the RK3328 once again is identical to the incarnation in
the RK3288 and the RK3399, except for where some of the configuration
and control registers are located in the GRF.

This adds the RK3328-specific logic necessary to reuse this driver.

Signed-off-by: David Wu <david.wu@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>