clk: renesas: r8a779g0: Add thermal clock

Add the module clock used by the Thermal Sensor/Chip Internal Voltage
Monitor/Core Voltage Monitor (THS/CIVM/CVM) on the Renesas R-Car V4H
(R8A779G0) SoC.

Based on a large patch in the BSP by Kazuya Mizuguchi.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/59461effd0d9f7a39e0c91352c87f2b7071b1891.1675958536.git.geert+renesas@glider.be