aspeed: add a FTGMAC100 nic

There is a second NIC but we do not use it for the moment. We use the
'aspeed' property to tune the definition of the end of ring buffer bit
for the Aspeed SoCs.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>