drm/msm/dsi: remove temp data from global pll structure

The 7nm, 10nm and 14nm drivers would store interim data used during
VCO/PLL rate setting in the global dsi_pll_Nnm structure. Move this data
structures to the onstack storage. While we are at it, drop
unused/static 'config' data, unused config fields, etc.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Tested-by: Stephen Boyd <swboyd@chromium.org> # on sc7180 lazor
Link: https://lore.kernel.org/r/20210331105735.3690009-23-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>