can: flexcan: add CAN-FD mode support

This patch adds CAN-FD mode support to the driver, it means that
payload size can extend up to 64 bytes.

Bit timing always set in the CBT register, not in the CTRL1 register any
more. This has an extend range of all CAN bit timing variables (PRESDIV,
PROPSEG, PSEG1, PSEG2 and RJW), which will improve the bit timing
accuracy.
Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
[mkl: move cbt-based bitrate support into separate function]
Link: https://lore.kernel.org/r/20200922144429.2613631-16-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>