net: add Faraday FTGMAC100 Gigabit Ethernet driver

FTGMAC100 Ethernet Media Access Controller supports 10/100/1000 Mbps
and MII/GMII.  This driver has been working on some ARM/NDS32 SoC's
including Faraday A369 and Andes AG102.

Signed-off-by: Po-Yu Chuang <ratbert@faraday-tech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>