tg3: Unlock 5717 B0+ support

This patch adjusts the driver to use the tg3_start_xmit_dma_bug()
transmit routine for all revisions of 5717 asic rev devices and then
allows the driver to attach to B0 and later devices.

Reviewed-by: Benjamin Li <benli@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>