dt-bindings: can: fsl,flexcan: add fsl,scu-index property to indicate a resource

For SoCs with SCU support, need setup stop mode via SCU firmware, so this
property can help indicate a resource in SCU firmware.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Link: https://lore.kernel.org/r/20201106105627.31061-3-qiangqing.zhang@nxp.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>