hfs/hfsplus: move on-disk layout declarations into hfs_common.h

hfs/hfsplus: move on-disk layout declarations into hfs_common.h

Currently, HFS declares on-disk layout's metadata structures
in fs/hfs/hfs.h and HFS+ declares it in fs/hfsplus/hfsplus_raw.h.
However, HFS and HFS+ on-disk layouts have some similarity and
overlapping in declarations. As a result, fs/hfs/hfs.h and
fs/hfsplus/hfsplus_raw.h contain multiple duplicated declarations.
Moreover, both HFS and HFS+ drivers contain completely similar
implemented functionality in multiple places.

This patch is moving the on-disk layout declarations from
fs/hfs/hfs.h and fs/hfsplus/hfsplus_raw.h into
include/linux/hfs_common.h with the goal to exclude
the duplication in declarations. Also, this patch prepares
the basis for creating a hfslib that can aggregate common
functionality without necessity to duplicate the same code
in HFS and HFS+ drivers.

Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
cc: Yangtao Li <frank.li@vivo.com>
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>