i965: Lower min/max after optimization on Gen4/5.

i965: Lower min/max after optimization on Gen4/5.

Gen4/5's SEL instruction cannot use conditional modifiers, so min/max
are implemented as CMP + SEL. Handling that after optimization lets us
CSE more.

On Ironlake:

   total instructions in shared programs: 6426035 -> 6422753 (-0.05%)
   instructions in affected programs: 326604 -> 323322 (-1.00%)
   helped: 1411

   total cycles in shared programs: 129184700 -> 129101586 (-0.06%)
   cycles in affected programs: 18950290 -> 18867176 (-0.44%)
   helped: 2419
   HURT: 328

Reviewed-by: Francisco Jerez <currojerez@riseup.net>