can: c_can: Add RAMINIT register information to driver data

Some platforms (e.g. TI) need special RAMINIT register handling.
Provide a way to store RAMINIT register description in driver data.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>