thermal/drivers/rcar_gen3: Document R-Car Gen4 and RZ/G2 support in driver comment

thermal/drivers/rcar_gen3: Document R-Car Gen4 and RZ/G2 support in driver comment

The R-Car Gen3 thermal driver supports both R-Car Gen3 and Gen4 SoCs
as well as RZ/G2. Update the driver comment. No functional change.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://patch.msgid.link/20251110143029.10940-1-marek.vasut+renesas@mailbox.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>