drm/amdgpu: cleanup comments in VM code

Neither the global nor the local mutex exists any more and
amdgpu doesn't support cayman.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
1 file changed