ath9k: implement IO serialization

This is a port of:
commit SHA1 6158425be398936af1fd04451f78ffad01529cb0
for 2.6.27

All 802.11n PCI devices (Cardbus, PCI, mini-PCI) require
serialization of IO when on non-uniprocessor systems. PCI
express devices not not require this.

This should fix our only last standing open ath9k kernel.org
bugzilla bug report:

http://bugzilla.kernel.org/show_bug.cgi?id=12110

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>