Add CAN node for imx8qm in devicetree.

Unlike on the i.MX 8QXP where the flexcan clocks are shared between
multiple CAN instances, the i.MX 8QM has separate flexcan clock slices.
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>