This patch make some of the blkfront structures a bit more C++ friendly. I am
creating a C++ version of the device private structure, and the goal here is to
convert it slowly until all or most fields are inside it. At that point, I
expect it to be easy to turn the functions into methods, etc. I am sorry, I
would really like to do a mass translation here, but there are urgent bugs
requiring my attention.

Some notes:
 * I am converting blkfront only, and leaving netfront with the old code. It
   shouldn't be hard, I just deferred the risk of mistakes to a future
   oportunity.
 * you will notice that lines that are added by me are not following the
   original file's identation. This is deliberate. As much as we have in our
   guidelines to preserve the original ident, since we are slowly converting
   those files, our identation should eventually win. Think of it as a form
   of cultural domination. (and shouldn't bother viewers if tabs=4 spaces)

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>