drm/msi/dsi: inline msm_dsi_pll_helper_clk_prepare/unprepare

10nm and 7nm already do not use these helpers, as they handle setting
slave DSI clocks after enabling VCO. Modify the rest of PHY drivers to
remove unnecessary indirection and drop enable_seq/disable_seq PLL
callbacks.

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/20210331105735.3690009-17-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Clark <robdclark@chromium.org>