Cycles microdisplacement: add max subdivision setting

This is to prevent situations such as when the camera gets very close to a mesh
and causes it to be tessellated into an excessive amount of micropolygons. In
REYES this is known as the eye-splits problem.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D1922

intern/cycles/blender/blender_sync.h

@@ -173,6 +173,7 @@ private:
 	bool is_cpu;
 
 	float dicing_rate;
+	int max_subdivisions;
 
 	struct RenderLayerInfo {
 		RenderLayerInfo()