dt-bindings: can: renesas,rcar-canfd: R-Car V3U is R-Car Gen4

Despite the name, R-Car V3U is the first member of the R-Car Gen4
family.  Hence generalize this by introducing a family-specific
compatible value for R-Car Gen4.

While at it, replace "both channels" by "all channels", as the numbers
of channels may differ from two.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/all/4dea4b7dd76d4f859ada85f97094b7adeef5169f.1674499048.git.geert+renesas@glider.be


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>