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.cpp

@@ -1000,7 +1000,7 @@ backend_instruction::has_side_effects() const
    case TCS_OPCODE_RELEASE_INPUT:
       return true;
    default:
-      return false;
+      return eot;
    }
 }