net: hix5hd2_gmac: add generic compatible string

The "hix5hd2" is SoC name, add the generic ethernet driver name.
The "hisi-gemac-v1" is the basic version and "hisi-gemac-v2" adds
the SG/TXCSUM/TSO/UFO features.

Signed-off-by: Dongpo Li <lidongpo@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>