s6gmac: xtensa s6000 on-chip ethernet driver

The s6000 on-chip MAC supports 10/100/1000Mbit and is connected to an
external PHY via MII or RGMII interface.

[jw@emlix.com: don't use device->bus_id directly]
Signed-off-by: Oskar Schirmer <os@emlix.com>
Signed-off-by: Daniel Glockner <dg@emlix.com>
Acked-by: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Johannes Weiner <jw@emlix.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Zankel <chris@zankel.net>