gfs2: read journal in large chunks to locate the head

Use bio(s) to read in the journal sequentially in large chunks and
locate the head of the journal.

This version addresses the issues Christoph pointed out w.r.t error handling
and using deprecated API.

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>

fs/gfs2/recovery.h

@@ -27,8 +27,6 @@ extern int gfs2_revoke_add(struct gfs2_jdesc *jd, u64 blkno, unsigned int where)
 extern int gfs2_revoke_check(struct gfs2_jdesc *jd, u64 blkno, unsigned int where);
 extern void gfs2_revoke_clean(struct gfs2_jdesc *jd);
 
-extern int gfs2_find_jhead(struct gfs2_jdesc *jd,
-		    struct gfs2_log_header_host *head);
 extern int gfs2_recover_journal(struct gfs2_jdesc *gfs2_jd, bool wait);
 extern void gfs2_recover_func(struct work_struct *work);
 extern int __get_log_header(struct gfs2_sbd *sdp,