IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping

IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping

When IOMMU mapping is failed, we issue a best effort rollback, stopping
IOMMU mapping, unmapping the previous IOMMU maps and then reporting the
error up to the call trees. When rollback is not feasible (in early
initialization phase or trade-off of complexity) for the hardware domain,
we do things on a best effort basis, only throwing out an error message.

IOMMU unmapping should continue despite an error, in an attempt to do
best effort cleanup.

Signed-off-by: Quan Xu <quan.xu@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>