tg3: Rename tg3 phy ID preprocessor definitions

The phylib presents the phy ID in a different format than the one tg3
has traditionally used.  To highlight the distinction, this patch
prepends the tg3 native phy ID format with TG3.

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