watchdog: aspeed: Move init to arch_initcall

Probing at device_initcall time lead to perverse cases where the
watchdog was probed after, say, I2C devices, which then leaves a
potentially running watchdog at the mercy of I2C device behaviour and
bus conditions.

Load the watchdog driver early to ensure that the kernel is patting it
well before initialising peripherals.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>