net: s6gmac: remove driver

The s6000 Xtensa support has been removed from the kernel in
4006e565. There are no other chips using this driver.

While the Mentor/Alcatel PE-MCXMAC IP core is also used in other
designs (Freescale Gianfar/UCC, QLogic NetXen, Solarflare, Agere
ET-1310, Netlogic XLR/XLS), none of these use this driver as it
heavily depends on the s6000 DMA engine. In fact, there is no
code sharing across any of the aforementioned devices.

Signed-off-by: Daniel Glöckner <dg@emlix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>