drm/amdgpu: unwrap fence chains in the explicit sync fence

Unwrap the explicit fence if it is a dma_fence_chain and
sync to the first fence not matching the owner rules.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210614174536.5188-1-christian.koenig@amd.com