can: drivers: add len8_dlc support for various CAN adapters

Support the Classical CAN raw DLC functionality to send and receive DLC values
from 9 .. 15 on various Classical CAN capable CAN network drivers:

- sja1000
- gs_usb
- pcan_usb
- pcan_usb_fd
- usb_8dev

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/r/20201111095923.2535-1-socketcan@hartkopp.net


[mkl: usb_8dev: changed indention]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>