MD: raid1 changes to allow use by device mapper

MD RAID1: Changes to allow RAID1 to be used by device-mapper (dm-raid.c)

Added the necessary congestion function and conditionalize calls requiring an
array 'queue' or 'gendisk'.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h
index 5fc4ca1..e743a64 100644
--- a/drivers/md/raid1.h
+++ b/drivers/md/raid1.h
@@ -126,4 +126,6 @@
  */
 #define	R1BIO_Returned 6
 
+extern int md_raid1_congested(mddev_t *mddev, int bits);
+
 #endif