drm/amd/amdgpu: switch on/off vcn power profile mode

switch to vcn power profile mode when a video is playing.
this can optimize the power/performance when the workload
is on the vcn.

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