watchdog: Allow building BCM7038_WDT for BCM63XX

CONFIG_BCM63XX denotes the legacy MIPS-based DSL SoCs which utilize the
same piece of hardware as a watchdog, make it possible to select that
driver for those platforms.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20211112224636.395101-5-f.fainelli@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>