can: m_can: m_can_chip_config(): enable and configure internal timestamps

This is a prerequisite for transitioning the m_can driver to rx-offload,
which works best with TX and RX timestamps.

The timestamps provided by M_CAN are 16-bit, timed according to the
nominal bit timing, and may be prescaled by a multiplier up to 16. We
choose the highest prescalar so that the timestamp wraps every 2^20 bit
times, or 209 ms at a bus speed of 5 Mbit/s. Timestamps will have a
precision of 16 bit times.

Link: https://lore.kernel.org/r/20210308102427.63916-3-torin@maxiluxsystems.com
Signed-off-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>