Introduce struct iommu_dev_data.use_vapic flag, which IOMMU driver
uses to determine if it should enable vAPIC support, by setting
the ga_mode bit in the device's interrupt remapping table entry.

Currently, it is enabled for all pass-through device if vAPIC mode
is enabled.
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>