Introducing a GEN6_FEAUTRES macro to simplify the struct definitions by
platforms given that most of the features are common. Inspired by the
GEN7_FEATURES macro done by Ben W. and others.
Use it for snb.
CC: Ben Widawsky <ben@bwidawsk.net> Signed-off-by: Carlos Santa <carlos.santa@intel.com> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>