thermal: rcar_gen3_thermal: Add r8a779a0 support

Add support for R-Car V3U. The new THCODE values are taken from the
example in the datasheet.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20201126223028.3119044-4-niklas.soderlund+renesas@ragnatech.se