common: Move get_ticks() function out of common.h

This function belongs in time.h so move it over and add a comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/broadcom/bcmstb/bcmstb.c b/board/broadcom/bcmstb/bcmstb.c
index 5fc2c05..23500df 100644
--- a/board/broadcom/bcmstb/bcmstb.c
+++ b/board/broadcom/bcmstb/bcmstb.c
@@ -6,6 +6,7 @@
  * Author: Thomas Fitzsimmons <fitzsim@fitzsim.org>
  */
 
+#include <time.h>
 #include <linux/types.h>
 #include <common.h>
 #include <env.h>