There is no dtsi file for msm8976 in the kernel sources. Drop the
compatibility with unofficial dtsi and remove support for handling the
single-cell calibration data on msm8976.

Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: NKonrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: NDmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: NAngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230101194034.831222-15-dmitry.baryshkov@linaro.orgSigned-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>