thermal/drivers/tsens: Sort out msm8976 vs msm8956 data

Tsens driver mentions that msm8976 data should be used for both msm8976
and msm8956 SoCs. This is not quite correct, as according to the
vendor kernels, msm8976 should use standard slope values (3200), while
msm8956 really uses the slope values found in the driver.

Add separate compatibility string for msm8956, move slope value
overrides to the corresponding init function and use the standard
compute_intercept_slope() function for both platforms.

Fixes: 0e580290

 ("thermal: qcom: tsens-v1: Add support for MSM8956 and MSM8976")
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230101194034.831222-7-dmitry.baryshkov@linaro.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>