rockchip: add timer driver

some rockchip soc will not include lib/timer.c in SPL stage,
so implement timer driver for some soc can use us delay function in SPL.

Signed-off-by: Lin Huang <hl@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/rk3288_common.h b/include/configs/rk3288_common.h
index a513ac4..af62227 100644
--- a/include/configs/rk3288_common.h
+++ b/include/configs/rk3288_common.h
@@ -22,7 +22,8 @@
 #define CONFIG_DISPLAY_BOARDINFO
 
 #define CONFIG_SYS_TIMER_RATE		(24 * 1000 * 1000)
-#define CONFIG_SYS_TIMER_COUNTER	(TIMER7_BASE + 8)
+#define	CONFIG_SYS_TIMER_BASE		0xff810020 /* TIMER7 */
+#define CONFIG_SYS_TIMER_COUNTER	(CONFIG_SYS_TIMER_BASE + 8)
 
 #define CONFIG_SPL_FRAMEWORK
 #define CONFIG_SPL_LIBCOMMON_SUPPORT