IPMI: new NMI handling

Convert over to the new NMI handling for getting IPMI watchdog timeouts via an
NMI.  This add config options to know if there is the ability to receive NMIs
and if it has an NMI post processing call.  Then it modifies the IPMI watchdog
to take advantage of this so that it can know if an NMI comes in.

It also adds testing that the IPMI NMI watchdog works.

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