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>
diff --git a/arch/arm/mach-imx/mx7/clock.c b/arch/arm/mach-imx/mx7/clock.c
index 0e08cab..75be4f8 100644
--- a/arch/arm/mach-imx/mx7/clock.c
+++ b/arch/arm/mach-imx/mx7/clock.c
@@ -7,6 +7,7 @@
  */
 
 #include <common.h>
+#include <clock_legacy.h>
 #include <div64.h>
 #include <asm/io.h>
 #include <linux/errno.h>