thermal/drivers/exynos: Stop using the threshold mechanism on Exynos 4210

Exynos 4210 supports setting a base threshold value, which is added to
all trip points. This might be useful, but is not really necessary in
our usecase, so we always set it to 0 to simplify the code a bit.

Additionally, this change makes it so that we convert the value to the
calibrated one in a slightly different place. This is more correct
morally, though it does not make any change when single-point
calibration is being used (which is the case currently).

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Mateusz Majewski <m.majewski2@samsung.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231201095625.301884-7-m.majewski2@samsung.com