hfsplus: add metadata file's clump size calculation functionality

There are situation when HFS+ volume had been created without
AttributesFile.  Such situation can take place because of using old
mkfs.hfs utility or creation HFS+ volume without taking in mind
necessity to use xattrs.  For example, Mac OS X 10.4 (Tiger) doesn't
create AttributesFile during mkfs phase.  Also it is a very frequent
situation for the case of users that created HFS+ volumes under Linux.
As a result, xattrs and POSIX ACLs on HFS+ volume are unavailable for
such users.

This patchset implements functionality of AttributesFile creation on
HFS+ volume in the case of this metadata file absence during operation
of xattr creation.

This patch:

Add functionality of metadata file's clump size calculation.  Operation
of AttributesFile creation needs in clump size setting.  This value will
be used when AttributesFile will be extended.

This code is adopted from code of newfs_hfs utility of diskdev_cmds packet
http://opensource.apple.com/tarballs/diskdev_cmds/

.

Signed-off-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hin-Tak Leung <htl10@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>