genirq/msi: Guard sysfs code

No point in building unused code when CONFIG_SYSFS=n.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211206210223.985907940@linutronix.de

include/linux/msi.h

@@ -239,9 +239,19 @@ void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
 void pci_msi_mask_irq(struct irq_data *data);
 void pci_msi_unmask_irq(struct irq_data *data);
 
+#ifdef CONFIG_SYSFS
 const struct attribute_group **msi_populate_sysfs(struct device *dev);
 void msi_destroy_sysfs(struct device *dev,
 		       const struct attribute_group **msi_irq_groups);
+#else
+static inline const struct attribute_group **msi_populate_sysfs(struct device *dev)
+{
+	return NULL;
+}
+static inline void msi_destroy_sysfs(struct device *dev, const struct attribute_group **msi_irq_groups)
+{
+}
+#endif
 
 /*
  * The arch hooks to setup up msi irqs. Default functions are implemented

kernel/irq/msi.c

@@ -72,6 +72,7 @@ void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
 }
 EXPORT_SYMBOL_GPL(get_cached_msi_msg);
 
+#ifdef CONFIG_SYSFS
 static ssize_t msi_mode_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
@@ -204,6 +205,7 @@ void msi_destroy_sysfs(struct device *dev, const struct attribute_group **msi_ir
 		kfree(msi_irq_groups);
 	}
 }
+#endif
 
 #ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
 static inline void irq_chip_write_msi_msg(struct irq_data *data,