i965/vs: Add instruction scheduling.

i965/vs: Add instruction scheduling.

While this is ignorant of dependency control, it's still good for a 0.39%
+/- 0.08% performance improvement on GLBenchmark 2.7 (n=548)

v2: Rewrite as a subclass of the base class for the FS instruction
    scheduler, inheriting the same latency information.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>