drm/msm/dp: drop unused fields from dp_power_private

Drop unused and obsolete fields from struct dp_power_private.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/576100/
Link: https://lore.kernel.org/r/20240126-dp-power-parser-cleanup-v3-2-098d5f581dd3@linaro.org