bitmaps.md: Convert to rST; move it into 'interop' dir

bitmaps.md: Convert to rST; move it into 'interop' dir

This is part of the on-going effort to convert QEMU upstream
documentation syntax to reStructuredText (rST).

The conversion to rST was done using:

    $ pandoc -f markdown -t rst bitmaps.md -o bitmaps.rst

Then, make a couple of small syntactical adjustments.  While at it,
reword a statement to avoid ambiguity.  Addressing the feedback from
this thread:

    https://lists.nongnu.org/archive/html/qemu-devel/2017-06/msg05428.html

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20170717105205.32639-2-kchamart@redhat.com
Signed-off-by: Jeff Cody <jcody@redhat.com>