drm/amd/display: Revert "init dispclk from bootup clock for DCN315"

drm/amd/display: Revert "init dispclk from bootup clock for DCN315"

[Why&How]
This reverts commit 14bb17cc37e0.
Due to the change, the display shows garbage on startup.

We have an alternative solution for the original issue:
d24203bb629f ("drm/amd/display: Re-check seamless boot can be enabled or not")

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Wang, Sung-huai <Danny.Wang@amd.com>
Signed-off-by: Matthew Stewart <matthew.stewart2@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>