i965: Implement proper workaround for Gen4 GPU CONSTANT_BUFFER hangs.

I finally managed to dig up some information on our mysterious GPU hangs.
A wiki page from the Crestline validation team mentions that they found
a GPU hang in "Serious Sam 2" (on Windows) with remarkably similar
conditions to the ones we've seen in Google Chrome and glmark2.

Apparently, if WM_STATE has "PS Use Source Depth" enabled, CC_STATE has
most depth state disabled, and you issue a CONSTANT_BUFFER command and
immediately draw, the depth interpolator makes a small mistake that
leads to hangs.

Most of the traces I looked at contained a CONSTANT_BUFFER packet
immediately followed by 3DPRIMITIVE, or at least very few packets.
It appears they also have "PS Use Source Depth" enabled - either at the
hang, or a little before it.  So I think this is our bug.

The workaround is to emit a non-pipelined state packet after issuing a
CONSTANT_BUFFER packet.  This is really similar to the workaround I
developed in commit c4fd0c9052dd391d6f2e9bb8e6da209dfc7ef35b.

v2: Fix word-wrapping issues.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Francisco Jerez <[email protected]>
Reviewed-by: Matt Turner <[email protected]>

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