ARM: multi_v7_defconfig: Enable BCM7038 Watchdog

The BCM7038 watchdog is used by all Broadcom STB SoCs but is not needed
for system reboot, we just turn it on as a module.

Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>