From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>

Fix up the 8259 ack handling for buggy SMM firmware.

See http://www.ussg.iu.edu/hypermail/linux/kernel/0203.2/0956.html

Apparently the embedded 8259A-compatible core is not fully functional.
This patch lets the I/O APIC-driven NMI watchdog to function correctly.
Credit to Ross Dickson for discovering this.