drm/amd/display: To apply the adjusted DP ref clock for DP devices

[Why]
For some pixel clock margin sensitive external monitor,
we could not keep original DP ref clock for the ASICs
supported SSC DP ref clock.

[How]
From slicon design team's comment,
we have to apply the adjusted DP ref clock for
DP devices.
DP 128b (DP2) signals uses the DTBCLK not DP ref.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Yiling Chen <yi-ling.chen2@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>