clk: renesas: rcar-gen3: Add SDnH clock

Currently a pass-through clock but we will make it a real divider clock
in the next patches.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20211110191610.5664-3-wsa+renesas@sang-engineering.com


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