arm64: dts: zii-ultra: adjust board names

Change ZII Ultra board names to be more in line with other ZII RDU platforms.

Signed-off-by: Ruslan Sushko <Ruslan.Sushko@zii.aero>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>