drivers: can: convert enum can_mode to a bit field

Convert the can_mode enum to a bit field to prepare for future extensions
(CAN-FD mode, transmitter delay compensation, one-shot mode, 3-samples
mode, ...).

Rename the existing modes:
- CAN_NORMAL_MODE   -> CAN_MODE_NORMAL
- CAN_SILENT_MODE   -> CAN_MODE_LISTENONLY
- CAN_LOOPBACK_MODE -> CAN_MODE_LOOPBACK

These mode names align with the Linux naming for CAN control modes.

The old CAN_SILENT_LOOPBACK_MODE can be set with the bitmask
(CAN_MODE_LISTENONLY | CAN_MODE_LOOPBACK).

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>