i965/shader: Don't use OptimizeForAOS for NIR vec4 vertex shaders

i965/shader: Don't use OptimizeForAOS for NIR vec4 vertex shaders

Shader-db results for vec4 programs using NIR on HSW:

   total instructions in shared programs: 1838157 -> 1828469 (-0.53%)
   instructions in affected programs:     275978 -> 266290 (-3.51%)
   helped:                                2827
   HURT:                                  244
   GAINED:                                0
   LOST:                                  0

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>