Some code cleanup, and fixing userspace builds after the last pull request.

I changed the functions in src/include/drv/app_dac_functions.c to static to fix an undefined reference issue after splitting the timing code into user/kernel headers. Everything else is just header guards.

src/fe/controllerAppUser.c

@@ -53,12 +53,12 @@
 
 #include "drv/epicsXfer.c" // User defined EPICS to/from FE data transfer function
 #include "drv/mapuser.h"
-#include "timing.c" // timing module / IRIG-B  functions
+#include "timing_common.h" // timing module / IRIG-B  functions
 
 #include "drv/inputFilterModule.h"
 #include "drv/inputFilterModule1.h"
-#include <drv/app_dac_functions.c>
-#include <drv/dac_info.c>
+#include "drv/app_dac_functions.c"
+#include "drv/dac_info.c"
 
 // #include "dolphin_usp.c"