can: rcar_canfd: Add support for r8a779a0 SoC

Adds support for the CANFD IP variant in the V3U SoC.

Differences to controllers in other SoCs are limited to an increase in
the number of channels from two to eight, an absence of dedicated
registers for "classic" CAN mode, and a number of differences in magic
numbers (register offsets and layouts).

Inspired by BSP patch by Kazuya Mizuguchi.

Link: https://lore.kernel.org/all/20220309162609.3726306-2-uli+renesas@fpond.eu
Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>