Make wait_for_device_probe() also do scsi_complete_async_scans()

Commit a7a20d103994 ("sd: limit the scope of the async probe domain")
make the SCSI device probing run device discovery in it's own async
domain.

However, as a result, the partition detection was no longer synchronized
by async_synchronize_full() (which, despite the name, only synchronizes
the global async space, not all of them).  Which in turn meant that
"wait_for_device_probe()" would not wait for the SCSI partitions to be
parsed.

And "wait_for_device_probe()" was what the boot time init code relied on
for mounting the root filesystem.

Now, most people never noticed this, because not only is it
timing-dependent, but modern distributions all use initrd.  So the root
filesystem isn't actually on a disk at all.  And then before they
actually mount the final disk filesystem, they will have loaded the
scsi-wait-scan module, which not only does the expected
wait_for_device_probe(), but also does scsi_complete_async_scans().

[ Side note: scsi_complete_async_scans() had also been partially broken,
  but that was fixed in commit 43a8d39d0137 ("fix async probe
  regression"), so that same commit a7a20d103994 had actually broken
  setups even if you used scsi-wait-scan explicitly ]

Solve this problem by just moving the scsi_complete_async_scans() call
into wait_for_device_probe().  Everybody who wants to wait for device
probing to finish really wants the SCSI probing to complete, so there's
no reason not to do this.

So now "wait_for_device_probe()" really does what the name implies, and
properly waits for device probing to finish.  This also removes the now
unnecessary extra calls to scsi_complete_async_scans().

Reported-and-tested-by: Artem S. Tashkinov <t.artem@mailcity.com>
Cc: Dan Williams <dan.j.williams@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: James Bottomley <jbottomley@parallels.com>
Cc: Borislav Petkov <bp@amd64.org>
Cc: linux-scsi <linux-scsi@vger.kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Remove scsi_wait_scan module

scsi_wait_scan was introduced with asynchronous host scanning as a hack
for distributions that weren't using proper udev based wait for root to
appear in their initramfs scripts.  In 2.6.30 Commit

c751085943362143f84346d274e0011419c84202
Author: Rafael J. Wysocki <rjw@sisk.pl>
Date:   Sun Apr 12 20:06:56 2009 +0200

    PM/Hibernate: Wait for SCSI devices scan to complete during resume

Actually broke scsi_wait_scan because it renders
scsi_complete_async_scans() a nop for modular SCSI if you include
scsi_scans.h (which this module does).

The lack of bug reports is sufficient proof that this module is no
longer used.

Cc: Jeff Mahoney <jeffm@suse.de>
Cc: Dave Jones <davej@redhat.com>
Cc: maximilian attems <max@stro.at>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Fix trace compiler warning
defconfig: enable some tracing

I'm not sure if I'll need these. Just picked the changes from Andromadus so I don't have to re-find them in case they prove to be needed at some point.