VT-d: relax source qualifier for MSI of phantom functions

With ordinary requests allowed to come from phantom functions, the
remapping tables ought to be set up to also allow for MSI triggers to
come from other than the "real" device.
---
As the numbering tries to indicate, this ought to go between the 6th
and 7th patch of the previously sent series.

--- a/xen/drivers/passthrough/vtd/intremap.c
+++ b/xen/drivers/passthrough/vtd/intremap.c
@@ -442,13 +442,22 @@ static void set_msi_source_id(struct pci
     devfn = pdev->devfn;
     switch ( pdev->type )
     {
+        unsigned int sq;
+
     case DEV_TYPE_PCIe_BRIDGE:
     case DEV_TYPE_PCIe2PCI_BRIDGE:
     case DEV_TYPE_LEGACY_PCI_BRIDGE:
         break;
 
     case DEV_TYPE_PCIe_ENDPOINT:
-        set_ire_sid(ire, SVT_VERIFY_SID_SQ, SQ_ALL_16, PCI_BDF2(bus, devfn));
+        switch ( pdev->phantom_stride )
+        {
+        case 1: sq = SQ_13_IGNORE_3; break;
+        case 2: sq = SQ_13_IGNORE_2; break;
+        case 4: sq = SQ_13_IGNORE_1; break;
+        default: sq = SQ_ALL_16; break;
+        }
+        set_ire_sid(ire, SVT_VERIFY_SID_SQ, sq, PCI_BDF2(bus, devfn));
         break;
 
     case DEV_TYPE_PCI: