can: m_can: make TXESC, RXESC config more explicit

Introduce masks for the three RXESC fields (RBDS, F1DS, F0DS) and the
one TXESC field (TBDS). Update m_can_chip_config() to explicitly set all
four fields to the 64-byte option (0x7) (and these defs are renamed to
be more concise).

This is an improvement in maintainability, and also makes it easier to
implement more flexible configuration of the M_CAN buffers in the
future.

Link: https://lore.kernel.org/r/20210504125123.500553-4-torin@maxiluxsystems.com


Signed-off-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>