Only pass to soong if PRODUCT_SET_DEBUGFS_RESTRICTIONS is defined

Bug: 432825073
Test: lunch factory_tegu-trunk_staging-user; \
      m out/target/product/tegu/vendor/build.prop
Test: lunch factory_tegu-trunk_staging-userdebug;\
      m out/target/product/tegu/vendor/build.prop
Test: lunch cf_x86_64_phone-trunk_staging-userdebug;\
      m out/target/product/vsoc_x86_64/vendor/build.prop
Change-Id: I626bfe50457f220a53559b9fffbed107d81e8bfd