mvebu: enable watchdog for Armada 37XX

mvebu: enable watchdog for Armada 37XX

This option includes support for watchdog timer on Marvell Armada 37xx
SoCs. [1] It is useful e.g. for Turris MOX, Marvell ESPRESSObin

Enable armada-37xx-watchdog driver as built in for mvebu cortex-a53,
so that kernel can start serving as soon as the driver is probed, until userspace takes over it.

[1] https://cateee.net/lkddb/web-lkddb/ARMADA_37XX_WATCHDOG.html

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
(improved commit message, 2nd paragraph)
Signed-off-by: Marek Behún <kabel@kernel.org>