drm/amd/display: Add debug support to override the Minimum DRAM Clock

[Why]
Requested feature to assist with Thermal, Acoustic, Power, and
Performance tuning.

[How]
Add a debug field that will override calculated minimum DRAM clock,
if the debug value is larger than the calculate value.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: David Galiffi <David.Galiffi@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>