drm/amdgpu: clean up UVD instance handling v2

The whole handle, filp and entity handling is superfluous here.

We should have reviewed that more thoughtfully. It looks like somebody
just made the code instance aware without knowing the background.

v2: fix one more missed case in amdgpu_uvd_suspend

Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>