i965: Replace cfg instances with calls to calculate_cfg().

i965: Replace cfg instances with calls to calculate_cfg().

Avoids regenerating it unnecessarily.

Every program in shader-db improved, none by an amount less than a 1/3
reduction. One Dota2 shader decreased from 62 -> 24.

cfg calculations:     429492 -> 193197 (-55.02%)

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>