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_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 1b97d1f..6db3b1c 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -2203,7 +2203,7 @@
 			      bytes[0], bytes[1]);
 		return false;
 	}
-	intel_sdvo->base.crtc_mask = (1 << 0) | (1 << 1);
+	intel_sdvo->base.crtc_mask = (1 << 0) | (1 << 1) | (1 << 2);
 
 	return true;
 }