drm/amdgpu: Avoid setting off KFD eviction fences in amdgpu_vm

Use FENCE_OWNER_KFD to synchronize PT/PD initialization and clearing
of page table entries. This avoids triggering KFD eviction fences on
the PD reservation objects of compute VMs.

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