drm/msm/dp: fold dp_power into dp_ctrl module

The dp_power submodule is limited to handling the clocks only following
previous cleanups. Fold it into the dp_ctrl submodule, removing one
unnecessary level of indirection.

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/576104/
Link: https://lore.kernel.org/r/20240126-dp-power-parser-cleanup-v3-5-098d5f581dd3@linaro.org