IOMMU: handle IOMMU mapping and unmapping failures

IOMMU: handle IOMMU mapping and unmapping failures

Treat IOMMU mapping and unmapping failures as a fatal to the DomU
If IOMMU mapping and unmapping failed, crash the DomU and propagate
the error up to the call trees.

No spamming of the log can occur. For DomU, we avoid logging any
message for already dying domains. For Dom0, that'll still be more
verbose than we'd really like, but it at least wouldn't outright
flood the console.

Signed-off-by: Quan Xu <quan.xu@intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>