watchdog: Add hardware dependency to BCM7038 driver

The BCM7038 watchdog driver is specific to Broadcom ARM and MIPS
SoCs so do not present it on other architectures, unless
build-testing.
Signed-off-by: NJean Delvare <jdelvare@suse.de>
Reviewed-by: NJustin Chen <justinpopo6@gmail.com>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>

drivers/watchdog/Kconfig

@@ -1380,10 +1380,12 @@ config BCM7038_WDT
 	tristate "BCM7038 Watchdog"
 	select WATCHDOG_CORE
 	depends on HAS_IOMEM
+	depends on ARCH_BRCMSTB || BMIPS_GENERIC || COMPILE_TEST
 	help
-	 Watchdog driver for the built-in hardware in Broadcom 7038 SoCs.
-
-	 Say 'Y or 'M' here to enable the driver.
+	 Watchdog driver for the built-in hardware in Broadcom 7038 and
+	 later SoCs used in set-top boxes.  BCM7038 was made public
+	 during the 2004 CES, and since then, many Broadcom chips use this
+	 watchdog block, including some cable modem chips.
 
 config IMGPDC_WDT
 	tristate "Imagination Technologies PDC Watchdog Timer"