dt-bindings: iommu: renesas,ipmmu-vmsa: R-Car V3U is R-Car Gen4

Despite the name, R-Car V3U is the first member of the R-Car Gen4
family.  Hence move its compatible value to the R-Car Gen4 section.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/c1fb71448a8400986fd30d51a1bb2704376c0306.1666361055.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>