can: flexcan: add more quirks to describe RX path capabilities

Most flexcan IP cores support 2 RX modes:
- FIFO
- mailbox

Some IP core versions cannot receive CAN RTR messages via mailboxes.
This patch adds quirks to document this.

This information will be used in a later patch to switch from FIFO to
more performant mailbox mode at the expense of losing the ability to
receive RTR messages. This trade off is beneficial in certain use
cases.

Link: https://lore.kernel.org/all/20220107193105.1699523-5-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>