common: Move clock functions into a new file

These three clock functions don't use driver model and should be migrated.
In the meantime, create a new file to hold them.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/board_f.c

@@ -11,6 +11,7 @@
 
 #include <common.h>
 #include <bloblist.h>
+#include <clock_legacy.h>
 #include <console.h>
 #include <cpu.h>
 #include <cpu_func.h>