drm/amd/amdgpu: Remove workaround check for UVD6 on APUs

On APUs the uvd6 driver was skipping proper suspend/resume routines resulting
in a broken state upon resume.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>