watchdog: bcm281xx: Fix Kconfig dependency

Use more the applicable ARCH_BCM_MOBILE option instead of ARCH_BCM as
dependency for bcm_kona_wdt.c.
Signed-off-by: Markus Mayer <markus.mayer@linaro.org>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/Kconfig

@@ -1168,7 +1168,7 @@ config BCM2835_WDT
 
 config BCM_KONA_WDT
 	tristate "BCM Kona Watchdog"
-	depends on ARCH_BCM
+	depends on ARCH_BCM_MOBILE
 	select WATCHDOG_CORE
 	help
 	  Support for the watchdog timer on the following Broadcom BCM281xx