cciss: read config to obtain max outstanding commands per controller

This patch changes the way we determine the maximum number of outstanding
commands for each controller.

Most Smart Array controllers can support up to 1024 commands, the notable
exceptions are the E200 and E200i.

The next generation of controllers which were just added support a mode of
operation called Zero Memory Raid (ZMR).  In this mode they only support
64 outstanding commands.  In Full Function Raid (FFR) mode they support
1024.

We have been setting the queue depth by arbitrarily assigning some value
for each controller.  We needed a better way to set the queue depth to
avoid lots of annoying "fifo full" messages.  So we made the driver a
little smarter.  We now read the config table and subtract 4 from the
returned value.  The -4 is to allow some room for ioctl calls which are
not tracked the same way as io commands are tracked.

Please consider this for inclusion.

Signed-off-by: Mike Miller <mike.miller@hp.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>