i965: Add norbc debug option

This INTEL_DEBUG option disables lossless compression (also known
as render buffer compression).

v2: (Matt) Use likely(!lossless_compression_disabled) instead of
           !likely(lossless_compression_disabled)
    (Grazvydas) Update docs/envvars.html

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

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

@@ -80,6 +80,7 @@ static const struct debug_control debug_control[] = {
    { "tes",         DEBUG_TES },
    { "l3",          DEBUG_L3 },
    { "do32",        DEBUG_DO32 },
+   { "norbc",       DEBUG_NO_RBC },
    { NULL,    0 }
 };