hv: vmsi: add vmsix on msi emulation support

Some passthrough devices require multiple MSI vectors, but don't
support MSI-X. In meanwhile, Linux kernel doesn't support continuous
vector allocation.
On native platform, this issue can be mitigated by IOMMU via interrupt
remapping. However, on ACRN, there is no vIOMMU.
vMSI-X on MSI emulation is one solution to mitigate this problem on ACRN.

This patch adds MSI-X emulation on MSI capability.
For the device needs to do MSI-X emulation, HV will hide MSI capability
and present MSI-X capability to guest.

The guest driver may need to modify to reqeust MSI-X vector.
For example:
        ret = pci_alloc_irq_vectors(pdev, 1, STMMAC_MSI_VEC_MAX,
-                                   PCI_IRQ_MSI);
+                                   PCI_IRQ_MSI | PCI_IRQ_MSIX);

To enable MSI-X emulation, the device should:
- 1. The device should be in vmsix_on_msi_devs array.
- 2. Support MSI, but don't support MSI-X.
- 3. MSI capability should support per-vector mask.
- 4. The device should have an unused BAR.
- 5. The device driver should not rely on PBA for functionality.

Tracked-On: #4831
Signed-off-by: Binbin Wu <binbin.wu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/hw/pci.c

@@ -767,6 +767,7 @@ struct pci_pdev *init_pdev(uint16_t pbdf, uint32_t drhd_index)
 
 			pdev->drhd_index = drhd_index;
 			num_pci_pdev++;
+			reserve_vmsix_on_msi_irtes(pdev);
 		} else {
 			pr_err("%s, %x:%x.%x unsupported headed type: 0x%x\n",
 				__func__, bdf.bits.b, bdf.bits.d, bdf.bits.f, hdr_type);