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/hisilicon/poplar/poplar.c b/board/hisilicon/poplar/poplar.c
index 4926419..304f64a 100644
--- a/board/hisilicon/poplar/poplar.c
+++ b/board/hisilicon/poplar/poplar.c
@@ -4,6 +4,7 @@
  * Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
  */
 
+#include <cpu_func.h>
 #include <dm.h>
 #include <common.h>
 #include <asm/io.h>