tg3: Convert u32 flag,flg2,flg3 uses to bitmap

Using a bitmap instead of separate u32 flags allows a consistent, simpler
and more extensible mechanism to determine capabilities.

Convert bitmasks to enum.
Add tg3_flag, tg3_flag_clear and tg3_flag_set.
Convert the flag & bitmask tests.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>