clk: renesas: r8a779h0: Add watchdog clock

Add the module clock used by the RCLK Watchdog Timer on the Renesas
R-Car V4M (R8A779H0) SoC.

Signed-off-by: Cong Dang <cong.dang.xn@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/f1dbf0f3f484015f2e629d78b746cf377d6f6746.1706790015.git.geert+renesas@glider.be