s390x/diag: Implement DIAG 320 subcode 1

DIAG 320 subcode 1 provides information needed to determine
the amount of storage to store one or more certificates from the
certificate store.

Upon successful completion, this subcode returns information of the current
cert store, such as the number of certificates stored and allowed in the cert
store, amount of space may need to be allocate to store a certificate,
etc for verification-certificate blocks (VCBs).

The subcode value is denoted by setting the left-most bit
of an 8-byte field.

The verification-certificate-storage-size block (VCSSB) contains
the output data when the operation completes successfully. A VCSSB
length of 4 indicates that no certificate are available in the cert
store.

Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260730214624.2328883-8-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>