drm/amdgpu: stop getting excl fence separately

Just grab all fences for the display flip in one go.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211028132630.2330-2-christian.koenig@amd.com