drm/i915: Make intel_detect_preproduction_hw easier to extend

As we add new generations, we should keep detecting new pre-production
system development platforms that were temporarily enabled to facilitate
initial development and now superseded by production systems. To make
it easier to add more platforms, split the if into a series of logical
operations.

v2: s/sdv/pre/ - not all system development vehicles are for
preproduction usage.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Zanoni, Paulo R" <paulo.r.zanoni@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170130104458.2653-1-chris@chris-wilson.co.uk
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -779,8 +779,12 @@ static void i915_workqueues_cleanup(struct drm_i915_private *dev_priv)
  */
 static void intel_detect_preproduction_hw(struct drm_i915_private *dev_priv)
 {
-	if (IS_HSW_EARLY_SDV(dev_priv) ||
-	    IS_SKL_REVID(dev_priv, 0, SKL_REVID_F0))
+	bool pre = false;
+
+	pre |= IS_HSW_EARLY_SDV(dev_priv);
+	pre |= IS_SKL_REVID(dev_priv, 0, SKL_REVID_F0);
+
+	if (pre)
 		DRM_ERROR("This is a pre-production stepping. "
 			  "It may not be fully functional.\n");
 }