watchdog: Add Apple SoC watchdog driver

Add support for the watchdog timer found in Apple SoCs. This driver is
also required to reboot these machines.

Signed-off-by: Sven Peter <sven@svenpeter.dev>
Tested-by: Janne Grunau <j@jannau.net>
Reviewed-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20211211123633.4392-2-sven@svenpeter.dev


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