i965: Add a driver hook for binding renderbuffers to textures.

i965: Add a driver hook for binding renderbuffers to textures.

This will let us use meta's acceleration from renderbuffers without having
to do a CopyTexImage first.

This is like what we do for TFP, but just taking an existing renderbuffer
and binding it to a texture with whatever its format was.  The
implementation won't work for stencil renderbuffers, and it only does
non-texture renderbuffers (but then, if you're using a texture
renderbuffer, you can just pull the texture object/level/slice out of the
renderbuffer, anyway).

v2: Don't forget to propagate NumSamples to the teximage.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>