net: macb: add support for sama7g5 emac interface

Add support for SAMA7G5 10/100Mbps interface.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>