drm/i915/guc: Don't enable GuC/HuC in auto mode on pre-Gen11

We are about to change default setting of "enable_guc" modparam
from 0(disabled) to -1(auto). As we only want to turn on
GuC/HuC on Gen11+, keep it off for older gens.

Note that it would be still possible to enable GuC/HuC on these
old platforms using explicit "enable_guc=2" modparam.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190712111445.21040-2-michal.wajdeczko@intel.com