arm, at91, wdt: make timeout configurable

make the HW WDT timeout configurable through the define
CONFIG_AT91_HW_WDT_TIMEOUT.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/README b/README
index a28ff13..ba57dc5 100644
--- a/README
+++ b/README
@@ -1257,6 +1257,9 @@
 		SoC, then define this variable and provide board
 		specific code for the "hw_watchdog_reset" function.
 
+		CONFIG_AT91_HW_WDT_TIMEOUT
+		specify the timeout in seconds. default 2 seconds.
+
 - U-Boot Version:
 		CONFIG_VERSION_VARIABLE
 		If this variable is defined, an environment variable