fec: use interrupt for MDIO completion indication

Queued for 2.6.36 in git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6.git

With the move to phylib (commit e6b043d5

) I was seeing sporadic "MDIO write
timeout" messages. Measure of the actual time spent showed latency times of
more than 1600us.

This patch uses the MII event indication of the FEC hardware to detect
completion of MDIO transactions.

BugLink: http://bugs.launchpad.net/bugs/546649
BugLink: http://bugs.launchpad.net/bugs/457878

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>