drm/i915: add pipe asserts for the crtc enable sequence

The i9xx modeset sequence is currently pretty fishy, so tight it all
up with some good assert-sprinkling.

We already have good coverage on the disable side, but the enable side
is spotty (since until recently it was wrong).

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -1474,6 +1474,8 @@ static void intel_enable_pll(struct drm_i915_private *dev_priv, enum pipe pipe)
 	int reg;
 	u32 val;
 
+	assert_pipe_disabled(dev_priv, pipe);
+
 	/* No really, not for ILK+ */
 	BUG_ON(!IS_VALLEYVIEW(dev_priv->dev) && dev_priv->info->gen >= 5);
 
@@ -1835,6 +1837,9 @@ static void intel_enable_pipe(struct drm_i915_private *dev_priv, enum pipe pipe,
 	int reg;
 	u32 val;
 
+	assert_planes_disabled(dev_priv, pipe);
+	assert_sprites_disabled(dev_priv, pipe);
+
 	if (HAS_PCH_LPT(dev_priv->dev))
 		pch_transcoder = TRANSCODER_A;
 	else