s390: Add attestation query information

We have information about the supported attestation header version
and plaintext attestation flag bits.
Let's expose it via the sysfs files.

Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/lkml/20220601100245.3189993-1-seiden@linux.ibm.com/


Signed-off-by: Janosch Frank <frankja@linux.ibm.com>