md: merge reconfig and check_reshape methods.

The difference between these two methods is artificial.
Both check that a pending reshape is valid, and perform any
aspect of it that can be done immediately.
'reconfig' handles chunk size and layout.
'check_reshape' handles raid_disks.

So make them just one method.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.h

@@ -326,7 +326,6 @@ struct mdk_personality
 	int (*check_reshape) (mddev_t *mddev);
 	int (*start_reshape) (mddev_t *mddev);
 	void (*finish_reshape) (mddev_t *mddev);
-	int (*reconfig) (mddev_t *mddev);
 	/* quiesce moves between quiescence states
 	 * 0 - fully active
 	 * 1 - no new requests allowed