VT-d: consider hidden devices when unmapping

VT-d: consider hidden devices when unmapping

Whether to clear an IOMMU's bit in the domain's bitmap should depend on
all devices the domain can control. For the hardware domain this
includes hidden devices, which are associated with DomXEN.

While touching related logic
- convert the "current device" exclusion check to a simple pointer
  comparison,
- convert "found" to "bool",
- adjust style and correct a typo in an existing comment.

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