can: mcp251xfd: add dev coredump support

For easier debugging this patch adds dev coredump support to the
driver. A dev coredump is generated in case the chip fails to start or
an error in the interrupt handler is detected.

The dev coredump consists of all chip registers and chip memory, as
well as the driver's internal state of the TEF-, RX- and TX-FIFOs, it
can be analyzed with the mcp251xfd-dump tool of the can-utils:

https://github.com/linux-can/can-utils/tree/master/mcp251xfd
Link: https://lore.kernel.org/r/20210304160328.2752293-2-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>