iommu/vt-d: Remove real DMA lookup in find_domain

iommu/vt-d: Remove real DMA lookup in find_domain

By removing the real DMA indirection in find_domain(), we can allow
sub-devices of a real DMA device to have their own valid
device_domain_info. The dmar lookup and context entry removal paths have
been fixed to account for sub-devices.

Fixes: 2b0140c69637 ("iommu/vt-d: Use pci_real_dma_dev() for mapping")
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20200527165617.297470-4-jonathan.derrick@intel.com
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207575
Signed-off-by: Joerg Roedel <jroedel@suse.de>