block: move capacity from disk to part0

Move disk->capacity to part0->nr_sects and convert all users who
directly accessed the field to use {get|set}_capacity().  This is done
early to allow the __dev field to be moved.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 9e866a2..1cf8281 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -138,7 +138,6 @@
 	struct block_device_operations *fops;
 	struct request_queue *queue;
 	void *private_data;
-	sector_t capacity;
 
 	int flags;
 	struct device *driverfs_dev;  // FIXME: remove
@@ -411,11 +410,11 @@
 }
 static inline sector_t get_capacity(struct gendisk *disk)
 {
-	return disk->capacity;
+	return disk->part0.nr_sects;
 }
 static inline void set_capacity(struct gendisk *disk, sector_t size)
 {
-	disk->capacity = size;
+	disk->part0.nr_sects = size;
 }
 
 #ifdef CONFIG_SOLARIS_X86_PARTITION