common: Move reset_cpu() to the CPU header

Move this function out of common.h and into a relevant header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/renesas/porter/porter.c b/board/renesas/porter/porter.c
index 86f79da..b9c2934 100644
--- a/board/renesas/porter/porter.c
+++ b/board/renesas/porter/porter.c
@@ -7,6 +7,7 @@
  */
 
 #include <common.h>
+#include <cpu_func.h>
 #include <env.h>
 #include <malloc.h>
 #include <dm.h>