forcedeth: remove device id macros

This patch removes the device id macros and instead uses the constants
directly.

The areas in which logic expressions where using the macros now instead
use feature/workaround flags.

No new functionality has been introduced in this patch, only clean up of
flags and macros.

Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>