drm/i915: check the power well on i915_pipe_enabled

This fixes "unclaimed register" messages when the power well is
disabled and there's a GPU hang.

v2: Use the new intel_display_power_enabled().
v3: Use the new domains for intel_display_power_enabled().
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -384,6 +384,10 @@ i915_pipe_enabled(struct drm_device *dev, int pipe)
 	enum transcoder cpu_transcoder = intel_pipe_to_cpu_transcoder(dev_priv,
 								      pipe);
 
+	if (!intel_display_power_enabled(dev,
+		POWER_DOMAIN_TRANSCODER(cpu_transcoder)))
+		return false;
+
 	return I915_READ(PIPECONF(cpu_transcoder)) & PIPECONF_ENABLE;
 }