s390/zcrypt: CEX7S exploitation support

This patch adds CEX7 exploitation support for the AP bus code,
the zcrypt device driver zoo and the vfio device driver.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>