s390/cpum_sf: correctly set the PID and TID in perf samples

The hardware sampler creates samples that are processed at a later
point in time.  The PID and TID values of the perf samples that are
created for hardware samples are initialized with values from the
current task.  Hence, the PID and TID values are not correct and
perf samples are associated with wrong processes.

The PID and TID values are obtained from the Host Program Parameter
(HPP) field in the basic-sampling data entries.  These PIDs are
valid in the init PID namespace.  Ensure that the PIDs in the perf
samples are resolved considering the PID namespace in which the
perf event was created.

To correct the PID and TID values in the created perf samples,
a special overflow handler is installed.  It replaces the default
overflow handler and does not become effective if any other
overflow handler is used.  With the special overflow handler most
of the perf samples are associated with the right processes.
For processes, that are no longer exist, the association might
still be wrong.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>