iommufd/selftest: Add IOMMU_TEST_OP_TRIGGER_VEVENT for vEVENTQ coverage

The handler will get vDEVICE object from the given mdev and convert it to
its per-vIOMMU virtual ID to mimic a real IOMMU driver.

Link: https://patch.msgid.link/r/1ea874d20e56d65e7cfd6e0e8e01bd3dbd038761.1741719725.git.nicolinc@nvidia.com


Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>