Document the compatible value for the Direct Memory Access Controller
blocks in the Renesas R-Car S4-8 (R8A779F0) SoC.

The most visible difference with DMAC blocks on other R-Car SoCs
(except R8A779A0) is the move of the per-channel registers to
a separate register block.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211222114507.1252947-2-yoshihiro.shimoda.uh@renesas.comSigned-off-by: Vinod Koul <vkoul@kernel.org>