drm/msm/dp: simplify stream clocks handling

There is only a single DP_STREAM_PM clock, stream_pixel. Instead of
using a separate dss_module_power instance for this single clock, handle
this clock directly. This allows us to drop several wrapping functions.

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/576102/
Link: https://lore.kernel.org/r/20240126-dp-power-parser-cleanup-v3-6-098d5f581dd3@linaro.org