xen/mcfg: Call PHYSDEVOP_pci_mmcfg_reserved for MCFG areas.

The PCI MMCONFIG area is usually reserved via the E820 so the Xen hypervisor
is aware of these regions. But they can also be enumerated in the ACPI
DSDT which means the hypervisor won't know of them until the initial
domain informs it of via PHYSDEVOP_pci_mmcfg_reserved.

This is what this patch does for all of the MCFG regions that the
initial domain is aware of (E820 enumerated and ACPI).

Reported-by:  Santosh Jodh <Santosh.Jodh@citrix.com>
CC: Jan Beulich <JBeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: David Vrabel <david.vrabel@citrix.com>
CC: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[v1: Redid it a bit]
[v2: Dropped the P2M 1-1 setting]
[v3: Check for Xen in-case we are running under baremetal]
[v4: Wrap with CONFIG_PCI_MMCONFIG]
diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
index 7000bb1..42721d1 100644
--- a/include/xen/interface/physdev.h
+++ b/include/xen/interface/physdev.h
@@ -231,6 +231,17 @@
 #define XEN_PCI_DEV_VIRTFN             0x2
 #define XEN_PCI_DEV_PXM                0x4
 
+#define XEN_PCI_MMCFG_RESERVED         0x1
+
+#define PHYSDEVOP_pci_mmcfg_reserved    24
+struct physdev_pci_mmcfg_reserved {
+    uint64_t address;
+    uint16_t segment;
+    uint8_t start_bus;
+    uint8_t end_bus;
+    uint32_t flags;
+};
+
 #define PHYSDEVOP_pci_device_add        25
 struct physdev_pci_device_add {
     /* IN */