[WATCHDOG] add bcm47xx watchdog driver

This add watchdog driver for broadcom 47xx device.
It uses the ssb subsytem to access embeded watchdog device.

Because the watchdog timeout is very short (about 2s), a soft timer is used
to increase the watchdog period.

Note : A patch for exporting the ssb_watchdog_timer_set will
be submitted on next linux-mips merge. Without this patch it can't 
be build as a module.

Signed-off-by: Aleksandar Radovanovic <biblbroks@sezampro.rs>
Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Tested-by: Florian Fainelli <florian@openwrt.org>
Cc: Ralf Baechle <ralf@linux-mips.org>                                                                                       
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index 70d7f8c..e8d45b6 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -729,6 +729,12 @@
 
 # MIPS Architecture
 
+config BCM47XX_WDT
+	tristate "Broadcom BCM47xx Watchdog Timer"
+	depends on BCM47XX
+	help
+	  Hardware driver for the Broadcom BCM47xx Watchog Timer.
+
 config RC32434_WDT
 	tristate "IDT RC32434 SoC Watchdog Timer"
 	depends on MIKROTIK_RB532