CMake: Enable WITH_USD by default

Having USD disabled by default was an oversight, and could have been
corrected earlier. It's already enabled by default in the
`blender_release.cmake` and `blender_full.cmake`.

CMakeLists.txt

@@ -278,7 +278,7 @@ option(WITH_ALEMBIC             "Enable Alembic Support" ON)
 option(WITH_ALEMBIC_HDF5        "Enable Legacy Alembic Support (not officially supported)" OFF)
 
 # Universal Scene Description support
-option(WITH_USD                 "Enable Universal Scene Description (USD) Support" OFF)
+option(WITH_USD                 "Enable Universal Scene Description (USD) Support" ON)
 
 # 3D format support
 # Disable opencollada when we don't have precompiled libs