tg3: Manage gphy power for CPMU-less devs only

This patch changes the code to only manage the PCIe gphy power for
CPMU-less devices only.  The CPMU takes over management for newer
chips.

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>