ARM: defconfig: update multi_v7_defconfig

Update the multi_v7_defconfig enabling the watchdog driver for Meson
SoCs.

Signed-off-by: Carlo Caione <carlo@caione.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>