DM9000: Use NSR to determine link-status on internal PHY

The DM9000_NSR register contains a copy of the internal PHY's
link status which we can use to determine if the link is up
or down. This eliminates the more costly (and sleeping) PHY
read when using the DM9000's own PHY.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>