hfs/hfsplus: rework debug output subsystem

hfs/hfsplus: rework debug output subsystem

Currently, HFS/HFS+ has very obsolete and inconvenient
debug output subsystem. Also, the code is duplicated
in HFS and HFS+ driver. This patch introduces
linux/hfs_common.h for gathering common declarations,
inline functions, and common short methods. Currently,
this file contains only hfs_dbg() function that
employs pr_debug() with the goal to print a debug-level
messages conditionally.

So, now, it is possible to enable the debug output
by means of:

echo 'file extent.c +p' > /proc/dynamic_debug/control
echo 'func hfsplus_evict_inode +p' > /proc/dynamic_debug/control

And debug output looks like this:

hfs: pid 5831:fs/hfs/catalog.c:228 hfs_cat_delete(): delete_cat: 00,48
hfs: pid 5831:fs/hfs/extent.c:484 hfs_file_truncate(): truncate: 48, 409600 -> 0
hfs: pid 5831:fs/hfs/extent.c:212 hfs_dump_extent():
hfs: pid 5831:fs/hfs/extent.c:214 hfs_dump_extent():  78:4
hfs: pid 5831:fs/hfs/extent.c:214 hfs_dump_extent():  0:0
hfs: pid 5831:fs/hfs/extent.c:214 hfs_dump_extent():  0:0

v4
Debug messages have been reworked and information about
new HFS/HFS+ shared declarations file has been added
to MAINTAINERS file.

v5
Yangtao Li suggested to clean up debug output and
fix several typos.

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
cc: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>