i965: Add norbc debug option

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>