i965: Move sampler state to state streaming.

i965: Move sampler state to state streaming.

Overall, across this series since the last set of numbers, gen6 3DMMES
taiji performance has dropped 0.8% +/- 0.3% (n=15), probably due to
the increased reissuing of state from some of the state objects that
otherwise never changed, and increased occurrence of the per-batch
overhead as we've increased how much we put in the batch BO without
increasing the batch BO's size.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>