iris: Use linear for exported resources if we can't convey tiling
If we have modifiers, we can use those to convey the tiling of exported resources. If we have the deprecated i915 GET/SET_TILING uAPI, we can use that to convey the tiling.
If we have neither, then we have to fall back to linear.
Closes: #6938 (closed)
Edited by Kenneth Graunke