USB: xHCI: Supporting MSI/MSI-X

Enable MSI/MSI-X supporting in xhci driver.

Provide the mechanism to fall back using MSI and Legacy IRQs
if MSI-X IRQs register failed.

Signed-off-by: Dong Nguyen <Dong.Nguyen@amd.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>,
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 6c7e343..5bc03d1 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1130,7 +1130,7 @@
 	int		page_size;
 	/* Valid values are 12 to 20, inclusive */
 	int		page_shift;
-	/* only one MSI vector for now, but might need more later */
+	/* msi-x vectors */
 	int		msix_count;
 	struct msix_entry	*msix_entries;
 	/* data structures */