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/silk/silk_spl.c b/board/renesas/silk/silk_spl.c
index 64ee75a..a2c397f 100644
--- a/board/renesas/silk/silk_spl.c
+++ b/board/renesas/silk/silk_spl.c
@@ -6,6 +6,7 @@
  */
 
 #include <common.h>
+#include <cpu_func.h>
 #include <malloc.h>
 #include <dm/platform_data/serial_sh.h>
 #include <asm/processor.h>