Ocfs2: Let ocfs2 support fiemap for symlink and fast symlink.

For fast symlink, it can be treated the same as inlined files since
the data extent we want to return of both case all were stored in
metadata block. For symlink, it can be simply treated the same as we
did for regular files.

Signed-off-by: Tristan Ye <tristan.ye@oracle.com>
Acked-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>