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/arch/sh/lib/time_sh2.c b/arch/sh/lib/time_sh2.c
index 14bef6b..d82c1d2 100644
--- a/arch/sh/lib/time_sh2.c
+++ b/arch/sh/lib/time_sh2.c
@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <time.h>
 #include <asm/io.h>
 #include <asm/processor.h>