i965: only allow SIMD8 kernel on sandybridge now

Until we fixed SIMD16 kernel, force to SIMD8 on sandybridge now.

src/mesa/drivers/dri/intel/intel_context.c

@@ -786,6 +786,11 @@ intelInitContext(struct intel_context *intel,
    if (INTEL_DEBUG & DEBUG_BUFMGR)
       dri_bufmgr_set_debug(intel->bufmgr, GL_TRUE);
 
+   /* XXX force SIMD8 kernel for Sandybridge before we fixed
+      SIMD16 interpolation. */
+   if (intel->gen == 6)
+       INTEL_DEBUG |= DEBUG_GLSL_FORCE;
+
    intel->batch = intel_batchbuffer_alloc(intel);
 
    intel_fbo_init(intel);