arm64: dts: imx8mq: increase NOC clock to 800 MHz

The NOC clock defaults to 400 MHz. Increase it to 800 MHz for improved
memory performance.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>