can: flexcan: allow to change quirks at runtime

This is a preparation patch for the upcoming support to change the
rx-rtr capability via the ethtool API.

Link: https://lore.kernel.org/all/20220107193105.1699523-3-mkl@pengutronix.de


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>