drivers: can: stm32: fdcan: enable hardware RX timestamping

Enables hardware RX timestamping for the STM32 FDCAN driver by
leveraging the M_CAN timestamping interface.

Introduces a new `timestamp-counter` property in the device tree binding.
If `CONFIG_CAN_RX_TIMESTAMP` is enabled and this property is defined,
the driver configures the M_CAN Timestamp Select to use the
external timestamp counter value.

This allows linking a Zephyr Counter device to the FDCAN instance to
provide precise packet timing.

Signed-off-by: Igor Knippenberg <knippenberg@filics.eu>