drm/i915: support 3 pipes on IVB+

Well almost anyway.  IVB has 3 planes, pipes, transcoders, and FDI
interfaces, but only 2 pipe PLLs.  So two of the pipes must use the same
pipe timings (e.g. 2 DP plus one other, or two HDMI with the same mode
and one other, etc.).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-By: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-By: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 3d73374..3009d2a 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2215,7 +2215,7 @@
 				  ironlake_panel_vdd_work);
 	}
 
-	intel_encoder->crtc_mask = (1 << 0) | (1 << 1);
+	intel_encoder->crtc_mask = (1 << 0) | (1 << 1) | (1 << 2);
 	connector->interlace_allowed = true;
 	connector->doublescan_allowed = 0;