drm/amdgpu/powerplay: provide the interface to disable uclk switch for DAL

provide the interface for DAL to disable uclk switch on navi10.
in this case, the uclk will be fixed to maximum.
this is a workaround when display configuration causes underflow issue.

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>