driver core: Introduce device_iommu_mapped() function

Some places in the kernel check the iommu_group pointer in
'struct device' in order to find out whether a device is
mapped by an IOMMU.

This is not good way to make this check, as the pointer will
be moved to 'struct dev_iommu_data'. This way to make the
check is also not very readable.

Introduce an explicit function to perform this check.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/device.h

@@ -1058,6 +1058,16 @@ static inline struct device *kobj_to_dev(struct kobject *kobj)
 	return container_of(kobj, struct device, kobj);
 }
 
+/**
+ * device_iommu_mapped - Returns true when the device DMA is translated
+ *			 by an IOMMU
+ * @dev: Device to perform the check on
+ */
+static inline bool device_iommu_mapped(struct device *dev)
+{
+	return (dev->iommu_group != NULL);
+}
+
 /* Get the wakeup routines, which depend on struct device */
 #include <linux/pm_wakeup.h>