i965/fs: Allow CSE on math opcodes on Gen6+.
i965/fs: Allow CSE on math opcodes on Gen6+.

total instructions in shared programs: 2081469 -> 2081248 (-0.01%)
instructions in affected programs:     22606 -> 22385 (-0.98%)
No programs were hurt by this patch.

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>
Reviewed-by: Chris Forbes <5dcac483e7a6e31a5cbe89f38cc69dff8ee93dac@ijw.co.nz>

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