IPMI: add polled interface

Currently the IPMI watchdog timer sets the watchdog timeout on a panic, but it
doesn't actually poll the interface to make sure the message goes out.

Add an interface for polling the IPMI driver, and add code to the IPMI
watchdog timer to poll the interface when the timer is set from a panic.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>