s390/pai: export number of sysfs attribute files

The number of sysfs files to be exported by the PAI device drivers
depends on the hardware version level. Use the value returned by
the hardware as the maximum number of counters to be exported
in the sysfs attribute tree.

Without the fix, older machine generation export counter names
based on paiXXXX_ctrnames static array info, which can be inaccurate,
as this array could also contain newer counter names in the
future.  This ensures proper pai counter sysfs attributes for
both newer generation and older generation processors.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>