wined3d public api cleanup

[Riccardo Bortolato]

Here is a follow up on the small fixes I sent the other day.

I'm storing the wined3d texture and sub level in the d3dX surfaces/volumes 
and this allows to go further with the removal of surfaces/volumes from the public api.

With these commits I also introduce a temporary function to handle mapping 
for surfaces and volumes which I hope it will gradually handle more of that 
eventually delegating only bound checks (and maybe other minor things) to helper functions.

Finally the remaining volume-related exported functions are removed.

What to do with buffers is still unclear to me.

Ciao,
Riccardo