Introduce a top-level 's390' directory which should be used when
adding new s390 specific debug feature files and/or directories.

This makes hopefully sure that the contents of the s390 directory will
be a bit more structured. Right now we have a couple of top-level
files where it is not easy to tell to which subsystem they belong to.
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

While sh previously had its own debugfs root, there now exists a
common arch_debugfs_dir prototype, so we switch everything over to
that.  Presumably once more architectures start making use of this
we'll be able to just kill off the stub kdebugfs wrapper.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>