support blackfin board initialization in generic board_f

- init hardware watchdog if applicable
- use CONFIG_SYS_MONITOR_LEN as the gd monitor len for Blackfin
- reserve u-boot memory at the top field of the RAM for Blackfin
- avoid refer to CONFIG_SYS_MONITOR_LEN, which is not defined by Blackfin

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
diff --git a/include/watchdog.h b/include/watchdog.h
index bd0a8d6..9273fa1 100644
--- a/include/watchdog.h
+++ b/include/watchdog.h
@@ -21,7 +21,8 @@
 int init_func_watchdog_reset(void);
 #endif
 
-#ifdef CONFIG_WATCHDOG
+#if defined(CONFIG_SYS_GENERIC_BOARD) && \
+	(defined(CONFIG_WATCHDOG) || defined(CONFIG_HW_WATCHDOG))
 #define INIT_FUNC_WATCHDOG_INIT	init_func_watchdog_init,
 #define INIT_FUNC_WATCHDOG_RESET	init_func_watchdog_reset,
 #else