oprofile, powerpc: Handle events that raise an exception without overflowing

oprofile, powerpc: Handle events that raise an exception without overflowing

Commit 5ddd8ab4b0ea75dc938f7c1437f4b081eaf1038d fixes a situation on POWER7
where events can roll back if a specualtive event doesn't actually complete.
This can raise a performance monitor exception.  We need to catch this to ensure
that we reset the PMC.  In all cases the PMC will be less than 256 cycles from
overflow.

This patch lifts Anton's fix for the problem in perf and applies it to oprofile
as well.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Cc: <stable@kernel.org> # as far back as it applies cleanly
Tested-by: Maynard Johnson <maynardj@us.ibm.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>