rtc: watchdog support for rtc-m41t80 driver

Add a watchdog driver interface to rtc-m41t80 driver.  This is derived from
works by Alexander Bigga <ab@mycable.de>

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Alexander Bigga <ab@mycable.de>
Cc: David Brownell <david-b@pacbell.net>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index fb9ce74..3593233 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -224,6 +224,13 @@
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-m41t80.
 
+config RTC_DRV_M41T80_WDT
+	bool "ST M41T80 series RTC watchdog timer"
+	depends on RTC_DRV_M41T80
+	help
+	  If you say Y here you will get support for the
+	  watchdog timer in ST M41T80 RTC chips series.
+
 comment "SPI RTC drivers"
 	depends on RTC_CLASS && SPI_MASTER