watchdog: npcm: Add support for WPCM450

Add a compatible string for WPCM450, which has essentially the same
watchdog mechanism as NPCM750.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210406120921.2484986-8-j.neuschaefer@gmx.net


Signed-off-by: Joel Stanley <joel@jms.id.au>