partitions: add ->set_capacity block device method

* Add ->set_capacity block device method and use it in rescan_partitions()
  to attempt enabling native capacity of the device upon detecting the
  partition which exceeds device capacity.

* Add GENHD_FL_NATIVE_CAPACITY flag to try limit attempts of enabling
  native capacity during partition scan.

Together with the consecutive patch implementing ->set_capacity method in
ide-gd device driver this allows automatic disabling of Host Protected Area
(HPA) if any partitions overlapping HPA are detected.

Cc: Robert Hancock <hancockrwd@gmail.com>
Cc: Frans Pop <elendil@planet.nl>
Cc: "Andries E. Brouwer" <Andries.Brouwer@cwi.nl>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Emphatically-Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/blkdev.h

@@ -1106,6 +1106,8 @@ struct block_device_operations {
 	int (*direct_access) (struct block_device *, sector_t,
 						void **, unsigned long *);
 	int (*media_changed) (struct gendisk *);
+	unsigned long long (*set_capacity) (struct gendisk *,
+						unsigned long long);
 	int (*revalidate_disk) (struct gendisk *);
 	int (*getgeo)(struct block_device *, struct hd_geometry *);
 	struct module *owner;