can: sja1000: Prepare the use of a threaded handler

In order to support a flavor of the sja1000 which sometimes freezes, it
will be needed upon certain interrupts to perform a soft reset. The soft
reset operation takes a bit of time, so better not do it within the hard
interrupt handler but rather in a threaded handler. Let's prepare the
possibility for sja1000_err() to request "interrupting" the current flow
and request the threaded handler to be run while keeping the interrupt
line low.

There is no functional change.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/all/20230616134553.2786391-1-miquel.raynal@bootlin.com


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