watchdog: Add support for Airoha EN7851 watchdog

Add support for Airoha EN7851 watchdog. This is a very basic watchdog
with no pretimeout support, max timeout is 28 seconds and it ticks based
on half the SoC BUS clock.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20241011104411.28659-2-ansuelsmth@gmail.com


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