ocfs2: Add journal_access functions with jbd2 triggers.

We create wrappers for ocfs2_journal_access() that are specific to the
type of metadata block.  This allows us to associate jbd2 commit
triggers with the block.  The triggers will compute metadata ecc in a
future commit.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>