tg3: Add 57766 device support.

The patch also adds a couple of fixes

 - For the 57766 and non Ax versions of 57765, bootcode needs to setup
   the PCIE Fast Training Sequence (FTS) value to prevent transmit hangs.
   Unfortunately, it does not have enough room in the selfboot case (i.e.
   devices with no NVRAM).  The driver needs to implement this.

 - For performance reasons, the 2k DMA engine mode on the 57766 should
   be enabled and dma size limited to 2k for standard sized packets.

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>