cmake remove circular linking and reorganize

- px4_add_module now requires MAIN
 - px4_add_library doesn't automatically link

src/modules/uORB/CMakeLists.txt

@@ -47,5 +47,5 @@ px4_add_module(
 		uORBManager.cpp
 		uORBUtils.cpp
 	DEPENDS
-		platforms__common
+		uorb_msgs
 	)

src/modules/uORB/uORB_tests/CMakeLists.txt

@@ -48,6 +48,5 @@ px4_add_module(
 		-Wno-sign-compare # TODO: fix all sign-compare
 	SRCS ${SRCS}
 	DEPENDS
-		platforms__common
 	)
-# vim: set noet ft=cmake fenc=utf-8 ff=unix :
+