drm/i915: Enable fastboot by default on VLV and CHV

We really want to have fastboot enabled by default to avoid an ugly
modeset during boot.

Currently we are enabling fastboot by default on gen9+ (Skylake and newer).
The intention is to enable it on older generations after it has seen more
testing on gen9+.

VLV and CHV devices are still being sold in stores today, as such it is
desirable to also enable fastboot by default on these now.

I've extensively tested fastboot=1 support on over 50 different
Bay- and Cherry-Trail devices. Testing DSI and eDP panels as well as
HDMI output (and even DP over Type-C on one device).

All 50 devices work fine with fastboot=1. On 2 devices their DSI panel
turns black as soon as the i915 driver loads when fastboot=0, so having
fastboot enabled is required for these 2 to work properly (for lack of
a better fix).

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190129142237.8684-1-hdegoede@redhat.com

drivers/gpu/drm/i915/intel_display.c

@@ -11735,7 +11735,15 @@ static bool fastboot_enabled(struct drm_i915_private *dev_priv)
 		return i915_modparams.fastboot;
 
 	/* Enable fastboot by default on Skylake and newer */
-	return INTEL_GEN(dev_priv) >= 9;
+	if (INTEL_GEN(dev_priv) >= 9)
+		return true;
+
+	/* Enable fastboot by default on VLV and CHV */
+	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
+		return true;
+
+	/* Disabled by default on all others */
+	return false;
 }
 
 static bool