> v2 coming soon with these changes and some additional comment cleanups.

So v1 + do_machine_check change is not surviving some real testing.  I'm injecting and
consuming errors sequentially with a small delay in between - so no fancy corner cases with
multiple errors being processed ... we get all the way done with one error before we start
the next.  Test only survives about 400ish recoveries before Linux dies complaining:
    "Timeout synchronizing machine check over CPUs". 
This probably means that some cpu wandered into the weeds and never showed up in the
handler.

patch just moves the recovery to the end of do_machine_check() instead of
doing the whole TIF_MCE_NOTIFY thing - and deletes all the TIF_MCE_NOTIFY
bits that are no longer needed.

-Tony