This patch fixes the following issues:

- fix a nasty corner case by which a task could inherit psr.pp/psr.up
  that could be stale by the time it runs. psr.pp/psr.up bits must be
  cleared on fork and inherited on execve(). Test case provided by
  John Levon.

- mask interrupts when locking the pfm stat structure. We don't want
  to take PMU interrupts in the middle of this kind of critical
  section.

- fix a bug in pfm_close() for context which use asynchronous
  notifications.  You cannot call fasync_helper() with interrupts
  disabled because it reenables them. There was no real danger of
  moving the call outside our critical section.

- fix a bug in in pfm_flush_pmds() where you can leave the freeze bit
  set in the pmc saved state.

- updated dump_pmu_state()

- cleanup the BUG_ON() usage