s390/cpumf: enable using AUX buffer

Modify PMU callback to use AUX buffer for diagnostic mode sampling.
Basic-mode sampling still use orignal way.

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