net: add support for STMicroelectronics Ethernet controllers.

This is the driver for the ST MAC 10/100/1000 on-chip Ethernet
controllers (Synopsys IP blocks).

Driver documentation:
 o http://stlinux.com/drupal/kernel/network/stmmac
Revisions:
 o http://stlinux.com/drupal/kernel/network/stmmac-driver-revisions
Performances:
 o http://stlinux.com/drupal/benchmarks/networking/stmmac

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>