arm, post: add missing post_time_ms for arm

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>

post/post.c

@@ -500,7 +500,7 @@ void post_reloc(void)
  */
 unsigned long post_time_ms(unsigned long base)
 {
-#ifdef CONFIG_PPC
+#if defined(CONFIG_PPC) || defined(CONFIG_ARM)
 	return (unsigned long)(get_ticks() / (get_tbclk() / CONFIG_SYS_HZ))
 		- base;
 #else