drm/msm/dp: tidy up platform data names

Follow the established symbol name pattern and rename platform data
structures.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/622213/
Link: https://lore.kernel.org/r/20241029-msm-dp-rename-v2-3-13c5c03fad44@linaro.org