cpr: relax vhost migration blockers

cpr: relax vhost migration blockers

vhost blocks migration if logging is not supported to track dirty
memory, and vhost-user blocks it if the log cannot be saved to a shm fd.

vhost-vdpa blocks migration if both hosts do not support all the device's
features using a shadow VQ, for tracking requests and dirty memory.

vhost-scsi blocks migration if storage cannot be shared across hosts,
or if state cannot be migrated.

None of these conditions apply if the old and new qemu processes do
not run concurrently, and if new qemu starts on the same host as old,
which is the case for cpr.

Narrow the scope of these blockers so they only apply to normal mode.
They will not block cpr modes when they are added in subsequent patches.

No functional change until a new mode is added.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <1698263069-406971-5-git-send-email-steven.sistare@oracle.com>