cmake remove circular linking and reorganize

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

src/systemcmds/pwm/CMakeLists.txt

@@ -39,6 +39,5 @@ px4_add_module(
 	SRCS
 		pwm.cpp
 	DEPENDS
-		platforms__common
 	)
-# vim: set noet ft=cmake fenc=utf-8 ff=unix :
+

src/systemcmds/pwm/pwm.cpp

@@ -63,7 +63,7 @@
 
 #include "systemlib/systemlib.h"
 #include "systemlib/err.h"
-#include "systemlib/param/param.h"
+#include <parameters/param.h>
 #include "drivers/drv_pwm_output.h"
 
 static void	usage(const char *reason);