[Why]
Drop hardcoded dispclk, dppclk, phyclk

[How]
Read the corresponding values from clock table entries already populated.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1403
Cc: stable@vger.kernel.org
Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>