On memory constrained hardware, tiling is vital for good performance as
it minimizes cache misses.  The downside is that for older hardware
(which often suffers from the lack of bandwidth) requires the use of
fences for many operations, which are in short supply and so may cause
shorter batchbuffers. However our batch buffers are typically short and
so this is unlikely to be a concern and not affect the performance wins.

A quick bit of testing suggests the effect is inconclusive on
firefox/i945:
                  linear            tiled
  xcb             205.470           206.219
  xcb-render-0.0  404.704           388.413
  xlib            166.410           170.805

A secondary effect of the patch is to workaround a G31 specific hang
when attempting to use linear 2048x2048 surfaces. Bonus!

Fixes:
  Bug 25375 - Performance issue using texture from pixmap (tfp) glx extension on 945
  http://bugs.freedesktop.org/show_bug.cgi?id=25375

  Bug 27100 - GPU Hung copying a 2048x1152 pixmap
  http://bugs.freedesktop.org/show_bug.cgi?id=27100



Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: John <jvinla@gmail.com>