drm/i915: add opregion function to notify bios of encoder enable/disable

The bios interface seems messy, and it's hard to tell what the bios
really wants. At first, only add support for DDI based machines (hsw+),
and see how it turns out.

The spec says to notify prior to power down and after power up. It is
unclear whether it makes a difference.

v2:
 - squash notification function and callers patches together (Daniel)
 - move callers to haswell_crtc_{enable,disable} (Daniel)
 - rename notification function (Chris)

v3:
 - separate notification function and callers again, as it's not clear
   whether the display power state notification is the right thing to do
   after all

v4: per Paulo's review:
 - drop LVDS
 - WARN on unsupported encoder types

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1fce841..3b7368d 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2189,15 +2189,23 @@
 extern void intel_i2c_reset(struct drm_device *dev);
 
 /* intel_opregion.c */
+struct intel_encoder;
 extern int intel_opregion_setup(struct drm_device *dev);
 #ifdef CONFIG_ACPI
 extern void intel_opregion_init(struct drm_device *dev);
 extern void intel_opregion_fini(struct drm_device *dev);
 extern void intel_opregion_asle_intr(struct drm_device *dev);
+extern int intel_opregion_notify_encoder(struct intel_encoder *intel_encoder,
+					 bool enable);
 #else
 static inline void intel_opregion_init(struct drm_device *dev) { return; }
 static inline void intel_opregion_fini(struct drm_device *dev) { return; }
 static inline void intel_opregion_asle_intr(struct drm_device *dev) { return; }
+static inline int
+intel_opregion_notify_encoder(struct intel_encoder *intel_encoder, bool enable)
+{
+	return 0;
+}
 #endif
 
 /* intel_acpi.c */