thermal/drivers/rcar_gen3: Add support for per-SoC default trim values

The Working Sample R-Car SoCs may not yet have thermal sensor trimming
values programmed into fuses, those fuses are blank instead. For such
SoCs, the driver includes fallback trimming values. Those values are
currently applied to all SoCs which use this driver.

Introduce support for per-SoC fallback trimming values in preparation
for SoCs which do not use these current trimming values. No functional
change is intended here.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20250625181739.28391-1-marek.vasut+renesas@mailbox.org