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/drivers/watchdog/ulp_wdog.c b/drivers/watchdog/ulp_wdog.c
index 313019f..7533fc6 100644
--- a/drivers/watchdog/ulp_wdog.c
+++ b/drivers/watchdog/ulp_wdog.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <cpu_func.h>
 #include <asm/io.h>
 #include <asm/arch/imx-regs.h>