sungem: Spring cleaning and GRO support

This patch simplifies the logic and locking in sungem significantly:

 - LLTX is gone, all private locks are gone, mutex is gone
 - We don't poll the PHY while the interface is down
 - The above allowed me to get rid of a pile of state flags
   using the proper interface state provided by the networking
   stack when needed and overall simplify the driver a lot
 - Allocate the bulk of RX skbs at init time using GFP_KERNEL
 - Fix a bug where the dev->features were set after register_netdev()
 - Added GRO while at it

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>