[TG3]: ASIC decoding and basic CPMU support.

Newer products change the way the ASIC revision is obtained.  This patch
implements how the driver will extract the revision number.

This patch also adds preliminary CPMU support.  CPMU stands for Central
Power Management Unit.  The CPMU's role is to put the chip into lower
power states when the operating conditions allow it.

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>