Move amdgpu_bo and related structures into amdgpu_object.h.

Move amdgpu_bo_list structures to the amdgpu_bo_list functions.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>