drm/amdgpu: promote the implicit sync to the dependent read fences

drm/amdgpu: promote the implicit sync to the dependent read fences

The driver doesn't want to implicitly sync on the DMA_RESV_USAGE_BOOKKEEP
usage fences, and the BOOKEEP fences should be synced explicitly. So, as
the VM implicit syncing only need to return and sync the dependent read
fences.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>