ARM: dts: aspeed: Remove undocumented wdt properties

The watchdog bindings do not describe an interrupt property nor clock
phandle, and the upstream driver never had code to use them. Drop them
from the device tree.

Also rename the node from wdt the more commonly used watchdog.

Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>