x86/PCI: Add to_pci_sysdata() helper

Various helpers need the pci_sysdata just to dereference a single field in
it.  Add a little helper that returns the properly typed sysdata pointer to
require a little less boilerplate code.

[jonathan.derrick: to_pci_sysdata const argument]
Link: https://lore.kernel.org/r/1579613871-301529-2-git-send-email-jonathan.derrick@intel.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

arch/x86/include/asm/pci.h

@@ -35,12 +35,15 @@ extern int noioapicreroute;
 
 #ifdef CONFIG_PCI
 
+static inline struct pci_sysdata *to_pci_sysdata(const struct pci_bus *bus)
+{
+	return bus->sysdata;
+}
+
 #ifdef CONFIG_PCI_DOMAINS
 static inline int pci_domain_nr(struct pci_bus *bus)
 {
-	struct pci_sysdata *sd = bus->sysdata;
-
-	return sd->domain;
+	return to_pci_sysdata(bus)->domain;
 }
 
 static inline int pci_proc_domain(struct pci_bus *bus)
@@ -52,24 +55,20 @@ static inline int pci_proc_domain(struct pci_bus *bus)
 #ifdef CONFIG_PCI_MSI_IRQ_DOMAIN
 static inline void *_pci_root_bus_fwnode(struct pci_bus *bus)
 {
-	struct pci_sysdata *sd = bus->sysdata;
-
-	return sd->fwnode;
+	return to_pci_sysdata(bus)->fwnode;
 }
 
 #define pci_root_bus_fwnode	_pci_root_bus_fwnode
 #endif
 
+#if IS_ENABLED(CONFIG_VMD)
 static inline bool is_vmd(struct pci_bus *bus)
 {
-#if IS_ENABLED(CONFIG_VMD)
-	struct pci_sysdata *sd = bus->sysdata;
-
-	return sd->vmd_domain;
-#else
-	return false;
-#endif
+	return to_pci_sysdata(bus)->vmd_domain;
 }
+#else
+#define is_vmd(bus)		false
+#endif /* CONFIG_VMD */
 
 /* Can be used to override the logic in pci_scan_bus for skipping
    already-configured bus numbers - to be used for buggy BIOSes
@@ -124,9 +123,7 @@ void native_restore_msi_irqs(struct pci_dev *dev);
 /* Returns the node based on pci bus */
 static inline int __pcibus_to_node(const struct pci_bus *bus)
 {
-	const struct pci_sysdata *sd = bus->sysdata;
-
-	return sd->node;
+	return to_pci_sysdata(bus)->node;
 }
 
 static inline const struct cpumask *