watchdog: Watchdog driver for Broadcom Set-Top Box

Watchdog driver for Broadcom 7038 and newer chips.

Signed-off-by: Justin Chen <justinpopo6@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>