i965: Add an option to not generate the SIMD8 fragment shader

For now, this can only be triggered with a new 'no8' INTEL_DEBUG option
and a new context flag.  We'll use the context flag later, but introducing
it now lets us bisect to this commit if it breaks something.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/intel_debug.c

@@ -66,6 +66,7 @@ static const struct dri_debug_control debug_control[] = {
    { "nodualobj", DEBUG_NO_DUAL_OBJECT_GS },
    { "optimizer", DEBUG_OPTIMIZER },
    { "noann", DEBUG_NO_ANNOTATION },
+   { "no8",  DEBUG_NO8 },
    { NULL,    0 }
 };