s390/uvdevice: Add 'List Secrets' UVC

s390/uvdevice: Add 'List Secrets' UVC

Userspace can call the List Secrets Ultravisor Call
using IOCTLs on the uvdevice. The List Secrets UV call lists the
identifier of the secrets in the UV secret store.

The uvdevice is merely transporting the request from userspace to
Ultravisor. It's neither checking nor manipulating the request or
response data.

Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20230615100533.3996107-5-seiden@linux.ibm.com
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Message-Id: <20230615100533.3996107-5-seiden@linux.ibm.com>