Document Renesas R-Car UFS host controller for R-Car S4-8 (r8a779f0).

Link: https://lore.kernel.org/r/20220603110524.1997825-2-yoshihiro.shimoda.uh@renesas.comReviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>