s390/cpuinfo: show facilities as reported by stfle

Add a new line to /proc/cpuinfo which shows all available facilities
as reported by the stfle instruction:

> cat /proc/cpuinfo
...
facilities      : 0 1 2 3 4 6 7 ...
...

Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>