tg3: Remove 5750 PCI code

The 5750 ASIC rev was never released as a PCI device.  It only exists as
a PCIe device.  This patch removes the code that supports the former
configuration.

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