fix a problem with bad performance after wakeup caused by r333321

This change reverts a "while here" part of r333321 that moved clearing
of suspended_cpus to an earlier place.

Apparently, there can be a problem when modifying (shared) memory before
restoring proper cache attributes. So, to be safe, move the clearing to
the old place.

Many thanks to Johannes Lundberg for bisecting the changes to that
particular commit and then bisecting the commit to the particular
change.

Reported by: many
Debugged by: Johannes Lundberg <johalun0@gmail.com>
MFC after: 1 week
X-MFC with: r333321