i965: Replace the region in DRIimage with just a BO pointer and stride.

i965: Replace the region in DRIimage with just a BO pointer and stride.

Regions aren't refcounted safely for multithreaded applications, and
they're not terribly useful wrappers of a BO, so I'm trying to remove
them.

Even the stride I added here could probably be reduced to use of an
existing field in the __DRIimageRec, but I want this to be as mechanical
of a change as possible.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>