arm64: dts: imx8mq-librem5: describe the clock for the csi sensors

The CLKO2 clock is used for both camera CSI interfaces as the
driving clock for the connected sensors. In order for it to be
available, use this hog. We can't simply add it to 2 different
sensor descriptions.

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>