can: flexcan: add CAN FD BRS support

This patch adds CAN FD BitRate Switch (BRS) support to driver.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Link: https://lore.kernel.org/r/20190712075926.7357-5-qiangqing.zhang@nxp.com


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