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/lager/lager.c b/board/renesas/lager/lager.c
index 3cb1a56..d6b388f 100644
--- a/board/renesas/lager/lager.c
+++ b/board/renesas/lager/lager.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <cpu_func.h>
 #include <env.h>
 #include <env_internal.h>
 #include <malloc.h>