clk: renesas: r8a779a0: Add the DU clock

The DU clock is added to the S3D1 clock parent. The Renesas BSP lists
S2D1 as the clock parent, however there is no S2 clock on this platform.

S3D1 is chosen as a best effort guess and demonstrates functionality but
is not guaranteed to be correct.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Link: https://lore.kernel.org/r/20210622232711.3219697-2-kieran.bingham@ideasonboard.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>