drm/amdgpu: use powerplay module for dgpu in Vi.

delete non-pp code and files. It was just a temporary
solution and not support dynamic power management.

Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Acked-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>