i965: Move fs_inst::has_side_effects()'s eot check to the parent class.

This eliminates a layer of wrapping, and makes a backend_instruction
sufficient.  The downside is that it exposes 'eot' to the vec4 backend,
which it doesn't need, but can basically happily ignore.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Pallavi G <pallavi.g@intel.com>

src/intel/compiler/brw_shader.h

@@ -167,6 +167,7 @@ struct backend_instruction {
    bool no_dd_check:1;
    bool saturate:1;
    bool shadow_compare:1;
+   bool eot:1;
 
    /* Chooses which flag subregister (f0.0 or f0.1) is used for conditional
     * mod and predication.