i965/fs: Drop our dead push constants before overflowing to pull constants.

i965/fs: Drop our dead push constants before overflowing to pull constants.

The idea of the original order was that you'd dead code eliminate accesses
to push constants.  But I've never seen a case of that (nor has
shader-db), while we frequently see sparse accesses of large constant
arrays that would overflow into pull constants.

Cuts pull constant use on csgo, serious sam, planeshift, and the cave:

total instructions in shared programs: 1695103 -> 1688795 (-0.37%)
instructions in affected programs:     92024 -> 85716 (-6.85%)
GAINED:                                339
LOST:                                  0

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