[S390] Add highgprs facility to /proc/cpuinfo

This patch makes the hwcap bit for the high gprs feature to be visible
in /proc/cpuinfo.

Signed-off-by: Andreas Krebbel <Andreas.Krebbel@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>