soc: renesas: R-Car V3U is R-Car Gen4

Despite the name, R-Car V3U is the first member of the R-Car Gen4
family.  Hence reflect this in the SoC Family field.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/2bbecad7b6c24c0d5c1797b3f7f0733d5ba33842.1651497066.git.geert+renesas@glider.be