drm/i915: Apply the force-detect VGA w/a to Valleyview

It appears that Valleyview shares its VGA encoder with more recent
siblings and requires the same forced detection cycle after a hardware
reset before we can rely on hotplugging.

Reported-and-tested-by: kobeqin <[e-mail]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67733
Tested-by: kobeqin <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
[danvet: Check for gen >= 5 insted, acked by Chris.]
Signed-off-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/i915/intel_crt.c

···
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crt *crt = intel_attached_crt(connector);
 
-	if (HAS_PCH_SPLIT(dev)) {
+	if (INTEL_INFO(dev)->gen >= 5) {
 		u32 adpa;
 
 		adpa = I915_READ(crt->adpa_reg);