bt: build unit tests only when CONFIG_BT_ENABLED=1

components/bt/test/component.mk

@@ -1,5 +1,5 @@
-#
-#Component Makefile
-#
-
+ifdef CONFIG_BT_ENABLED
 COMPONENT_ADD_LDFLAGS = -Wl,--whole-archive -l$(COMPONENT_NAME) -Wl,--no-whole-archive
+else
+COMPONENT_CONFIG_ONLY := 1
+endif