intel: Rebuild PBO blit glTexImage() on top of miptrees.

intel: Rebuild PBO blit glTexImage() on top of miptrees.

This will ensure that we have resolves if we ever extend this to
glTexSubImage(), and fixes missing image start offset handling.

The texture buffer alloc ended up getting moved up, because we want to
look at the format of the image's actual mt to see if we'll end up
blitting the right thing, in the case of packed depth/stencil uploads.

This is the last caller of intelEmitCopyBlit() on a miptree-wrapped BO.

Reviewed-and-tested-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Paul Berry <stereotype441@gmail.com>