watchdog: add timeout-sec property binding

this patchset add the timeout-sec property to the following drivers:
orion_wdt, pnx4008_wdt, s3c2410_wdt and at91sam9_wdt.

The at91sam9_wdt is tested on evk-pr3,
the other drivers are compile tested only.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Wolfram Sang <w.sang@pengutronix.de>
Cc: Masanari Iida <standby24x7@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Andrew Victor <linux@maxim.org.za>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>