ocfs2: Move directory manipulation code into dir.c

The code for adding, removing, deleting directory entries was splattered all
over namei.c. I'd rather have this all centralized, so that it's easier to
make changes for inline dir data, and eventually indexed directories.

None of the code in any of the functions was changed. I only removed the
static keyword from some prototypes so that they could be exported.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Reviewed-by: Joel Becker <joel.becker@oracle.com>