can: bxcan: add support for ST bxCAN controller

Add support for the basic extended CAN controller (bxCAN) found in many
low- to middle-end STM32 SoCs. It supports the Basic Extended CAN
protocol versions 2.0A and B with a maximum bit rate of 1 Mbit/s.

The controller supports two channels (CAN1 as primary and CAN2 as
secondary) and the driver can enable either or both of the channels. They
share some of the required logic (e. g. clocks and filters), and that means
you cannot use the secondary CAN without enabling some hardware resources
managed by the primary CAN.

Each channel has 3 transmit mailboxes, 2 receive FIFOs with 3 stages and
28 scalable filter banks.
It also manages 4 dedicated interrupt vectors:
- transmit interrupt
- FIFO 0 receive interrupt
- FIFO 1 receive interrupt
- status change error interrupt

Driver uses all 3 available mailboxes for transmission and FIFO 0 for
reception. Rx filter rules are configured to the minimum. They accept
all messages and assign filter 0 to CAN1 and filter 14 to CAN2 in
identifier mask mode with 32 bits width. It enables and uses transmit,
receive buffers for FIFO 0 and error and status change interrupts.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20230328073328.3949796-6-dario.binacchi@amarulasolutions.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>