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/technexion/pico-imx7d/spl.c b/board/technexion/pico-imx7d/spl.c
index 8955622..6c432ca 100644
--- a/board/technexion/pico-imx7d/spl.c
+++ b/board/technexion/pico-imx7d/spl.c
@@ -5,6 +5,7 @@
  * Author: Richard Hu <richard.hu@technexion.com>
  */
 
+#include <cpu_func.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/crm_regs.h>