[TG3]: Disable GPHY autopowerdown

New CPMU devices contend with the GPHY for power management.  The GPHY
autopowerdown feature is enabled by default in the PHY and thus needs to
be disabled after every PHY reset.

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