intel: Defer tiling change to allocation.

As we now expose a method to allocate tiled buffers, it makes more sense
to defer the SET_TILING until required. Besides the slim chance that it
will be a no-op, by delaying the change we are less likely to stall on
waiting for a bound buffer to release a fence register.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>