Cycles: Make not-compact BVH the default for embree

Measurements shown on average a 1.08x speedup for a 1.04x increase in
memory usage which is an acceptable trade off for a default setting,
although discoverability of such settings influencing memory usage could
be improved.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D15429

intern/cycles/blender/addon/properties.py

@@ -693,7 +693,7 @@ class CyclesRenderSettings(bpy.types.PropertyGroup):
     debug_use_compact_bvh: BoolProperty(
         name="Use Compact BVH",
         description="Use compact BVH structure (uses less ram but renders slower)",
-        default=True,
+        default=False,
     )
     debug_bvh_time_steps: IntProperty(
         name="BVH Time Steps",