x86, NMI: Remove DIE_NMI_IPI

With priorities in place and no one really understanding the difference between
DIE_NMI and DIE_NMI_IPI, just remove DIE_NMI_IPI and convert everyone to DIE_NMI.

This also simplifies default_do_nmi() a little bit.  Instead of calling the
die_notifier in both the if and else part, just pull it out and call it before
the if-statement.  This has the side benefit of avoiding a call to the ioport
to see if there is an external NMI sitting around until after the (more frequent)
internal NMIs are dealt with.

Patch-Inspired-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1294348732-15030-5-git-send-email-dzickus@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>