Documentation: virt: Protected virtual machine dumps

Let's add a documentation file which describes the dump process. Since
we only copy the UV dump data from the UV to userspace we'll not go
into detail here and let the party which processes the data describe
its structure.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20220517163629.3443-10-frankja@linux.ibm.com


Message-Id: <20220517163629.3443-10-frankja@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>