UPSTREAM: net: ethernet: arc: Keep emac compatibility for more Rockchip SoCs

UPSTREAM: net: ethernet: arc: Keep emac compatibility for more Rockchip SoCs

On the RK3066/RK3188, there was fixed GRF offset configuration to set emac
and fixed DIV2 mac TX/RX clock. So, we need to easily set and fit to other
SoCs (RK3036) which maybe have different GRF offset, and need adjust mac
TX/RX clock.

Change-Id: Ic130da39af5cc585974c9231f80472fa2a15a29b
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
(cherry picked from git.kernel.org next/linux-next.git master
 commit f4c9d3ee0334fd9c6c8f2c3a8bd7d0841880e127)