tg3: Migrate phy preprocessor defs to system defs

This patch changes to code to use some of the preprocessor
definitions from mii.h over its homegrown equivalents.

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