Add support for bxcan (Basic eXtended CAN controller) to STM32F746. The
chip contains three CAN peripherals, CAN1 and CAN2 in dual peripheral
configuration and CAN3 in single peripheral configuration:
- Dual CAN peripheral configuration:
  * CAN1: Primary bxCAN for managing the communication between a secondary
    bxCAN and the 512-byte SRAM memory.
  * CAN2: Secondary bxCAN with no direct access to the SRAM memory.
  This means that the two bxCAN cells share the 512-byte SRAM memory and
  CAN2 can't be used without enabling CAN1.
- Single CAN peripheral configuration:
  * CAN3: Primary bxCAN with dedicated Memory Access Controller unit and
    512-byte SRAM memory.

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| features | CAN1              | CAN2               | CAN 3               |
 -------------------------------------------------------------------------
| SRAM     | 512-byte shared between CAN1 & CAN2    | 512-byte            |
 -------------------------------------------------------------------------
| Filters  | 26 filters shared between CAN1 & CAN2  | 14 filters          |
 -------------------------------------------------------------------------
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/all/20230427204540.3126234-6-dario.binacchi@amarulasolutions.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>