net: hisilicon: Add Fast Ethernet MAC driver

This patch adds the Hisilicon Fast Ethernet MAC(FEMAC) driver.
The FEMAC supports max speed 100Mbps and has been used in many
Hisilicon SoC.

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