drm/msm/dsi: move all PLL callbacks into PHY config struct

Move all PLL-related callbacks into struct msm_dsi_phy_cfg. This limits
the amount of data in the struct msm_dsi_pll.

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/20210331105735.3690009-7-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>