can: m_can: Write transmit header and data in one transaction

Combine header and data before writing to the transmit fifo to reduce
the overhead for peripheral chips.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/all/20240207093220.2681425-4-msp@baylibre.com


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