drm/amd/display: move back vbios cmd table for set dprefclk

drm/amd/display: move back vbios cmd table for set dprefclk

[Why]
Upon closer inspection, our previous implementation is missing
code for programming de-spread and DP DTO. Porting this logic
into driver is rather involved, as there are a lot of table
look ups. So for now move back to calling vbios cmd table

[How]
Go back to calling vbios cmd table for set dp_refclk

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>