can: gs_usb: add CAN-FD support

can: gs_usb: add CAN-FD support

CANtact Pro from Linklayer is the first gs_usb compatible device
supporting CAN-FD with a different HW and re-written candlelight FW.

Support for CAN-FD is indicated by the device setting the
GS_CAN_FEATURE_FD flag. CAN-FD support is requested by the driver with
the GS_CAN_MODE_FD flag. The CAN-FD specific data bit timing
parameters are set with the GS_USB_BREQ_DATA_BITTIMING control
message.

This patch is based on the Eric Evenchick's gs_usb_fd driver (which
itself is a fork of gs_usb). The gs_usb_fd code base was reintegrated
into the gs_usb driver, and reworked to not break the existing
classical-CAN only hardware.

Link: https://lore.kernel.org/all/20220309124132.291861-16-mkl@pengutronix.de
Link: https://github.com/linklayer/gs_usb_fd/issues/2
Co-developed-by: Eric Evenchick <eric@evenchick.com>
Signed-off-by: Eric Evenchick <eric@evenchick.com>
Signed-off-by: Peter Fink <pfink@christ-es.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>