drm/amd/display: Set dispclk and dprefclock directly

[Why]
To simply logic for setting DCN specific clocks, we will send
SMU message directly through the VBIOS message box.

[How]
Add new structure in pp_smu to hold functions to set clocks
through vbios message box

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>