drm/amdgpu: find partition ID when open device

Find partition ID when open device from render device minor.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-and-tested-by: Philip <Yang&lt;Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>