dt-bindings: mmc: renesas,sdhi: Document RZ/V2L SoC

Document RZ/V2L SDHI bindings. RZ/V2L SDHI is almost identical to one
found on the R-Car Gen3. No driver changes are required as generic
compatible string "renesas,rcar-gen3-sdhi" will be used as a fallback.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220227212330.22262-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>