watchdog: Add support for Armada 37xx CPU watchdog

watchdog: Add support for Armada 37xx CPU watchdog

This adds support for the CPU watchdog found on Marvell Armada 37xx
SoCs.

There are 4 counters which can be set as CPU watchdog counters.
This driver uses the second counter (ID 1, counting from 0) as watchdog
counter, and first counter (ID 0) to implement pinging on the second
counter without the need to disable it.

Since counters IDs 2 and 3 are enabled already before even U-Boot
starts, this driver does not use them at all, for example by adding a
device tree property for counter selection.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>