i965: Set tiling on BOs imported with modifiers

We need this to ensure that GTT maps work on buffers we get from Vulkan
on the off chance that someone does a readpixels or something.  Soon, we
will be removing GTT maps from i965 entirely and this can be reverted.
None the less, it's needed for stable.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit 50485723)