AMD IOMMU: add device reference counting for protection domains

Impact: know how many devices are assigned to a domain

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/x86/include/asm/amd_iommu_types.h

@@ -203,6 +203,7 @@ struct protection_domain {
 	int mode;		/* paging mode (0-6 levels) */
 	u64 *pt_root;		/* page table root pointer */
 	unsigned long flags;	/* flags to find out type of domain */
+	unsigned dev_cnt;	/* devices assigned to this domain */
 	void *priv;		/* private data */
 };