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/arch/sh/cpu/sh4/watchdog.c b/arch/sh/cpu/sh4/watchdog.c
index 7c157bc..1de32cd 100644
--- a/arch/sh/cpu/sh4/watchdog.c
+++ b/arch/sh/cpu/sh4/watchdog.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+
 
 #include <common.h>
+#include <cpu_func.h>
 #include <asm/processor.h>
 #include <asm/system.h>
 #include <asm/io.h>