netdev: bfin_mac: fix performance issue found by netperf

- Remove dead long delay
- Use proper defines
- Remove broken implementation of the TX DMA Data Alignment TXDWA feature

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>