net: ethernet: arc: Add support emac for RK3036

The RK3036's GRFs offset are different with RK3066/RK3188, and need to set
mac TX/RX clock before probe emac.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>