drm/msm/dsi: make save/restore_state phy-level functions

Morph msm_dsi_pll_save/restore_state() into msm_dsi_phy_save/restore_state(),
thus removing last bits of knowledge about msm_dsi_pll from dsi_manager.

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/20210331105735.3690009-14-dmitry.baryshkov@linaro.org


Signed-off-by: Rob Clark <robdclark@chromium.org>