net-next: mediatek: cleanup unnecessary get chip id and its user

Since driver is devicetree-based, all device type and charateristic can be
determined by the compatible string and its data. It's unnecessary to
create another dependent function to check chip ID and then decide whether
the specific funciton is being supported on a certain device. It can be
totally replaced by the existing flag, so a cleanup is made by removing
the function and the only user, HWLRO.

MT2701 also have a missing HWLRO support in old code, so add it the same
patch.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>