vfio-ccw: Rearrange pfn_array and pfn_array_table arrays

vfio-ccw: Rearrange pfn_array and pfn_array_table arrays

While processing a channel program, we currently have two nested
arrays that carry a slightly different structure.  The direct CCW
path creates this:

  ccwchain->pfn_array_table[1]->pfn_array[#pages]

while an IDA CCW creates:

  ccwchain->pfn_array_table[#idaws]->pfn_array[1]

The distinction appears to state that each pfn_array_table entry
points to an array of contiguous pages, represented by a pfn_array,
um, array.  Since the direct-addressed scenario can ONLY represent
contiguous pages, it makes the intermediate array necessary but
difficult to recognize.  Meanwhile, since an IDAL can contain
non-contiguous pages and there is no logic in vfio-ccw to detect
adjacent IDAWs, it is the second array that is necessary but appearing
to be superfluous.

I am not aware of any documentation that states the pfn_array[] needs
to be of contiguous pages; it is just what the code does today.
I don't see any reason for this either, let's just flip the IDA
codepath around so that it generates:

  ch_pat->pfn_array_table[1]->pfn_array[#idaws]

This will bring it in line with the direct-addressed codepath,
so that we can understand the behavior of this memory regardless
of what type of CCW is being processed.  And it means the casual
observer does not need to know/care whether the pfn_array[]
represents contiguous pages or not.

NB: The existing vfio-ccw code only supports 4K-block Format-2 IDAs,
so that "#pages" == "#idaws" in this area.  This means that we will
have difficulty with this overlap in terminology if support for
Format-1 or 2K-block Format-2 IDAs is ever added.  I don't think that
this patch changes our ability to make that distinction.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20190606202831.44135-6-farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>