s390/uv: Provide host-key hashes in sysfs

s390/uv: Provide host-key hashes in sysfs

Utilize the new Query Ultravisor Keys UVC to give user space the
information which host-keys are installed on the system.

Create a new sysfs directory 'firmware/uv/keys' that contains the hash
of the host-key and the backup host-key of that system. Additionally,
the file 'all' contains the response from the UVC possibly containing
more key-hashes than currently known.

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Link: https://lore.kernel.org/r/20241023075529.2561384-1-seiden@linux.ibm.com
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>