thermal: rcar_gen3_thermal: Store thcode and ptat in priv data

Prepare for reading the THCODE and PTAT values from hardware fuses by
storing the values used during calculations in the drivers private
data structures.

As the values are now stored directly in the private data structures
there is no need to keep track of the TSC channel id as its only usage
was to lookup the THCODE row, drop it.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211014103816.1939782-2-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>