[IA64] perfmon.c: cleanup system-wide context when closed from another cpu

[IA64] perfmon.c: cleanup system-wide context when closed from another cpu

- fix pfm_stop() and pfm_flush_pmds() to correctly cleanup
  in case of a system-wide context which is closed while running
  from another processor. This was leading to an assertion failure
  in pfm_loads_regs() for the next user of the PMU on the monitored
  CPU.

signed-off-by: stephane eranian <eranian@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>