drm/amdgpu: vm flush needed after updating PDEs

If page table PDEs is evicted and restored, after updating PDEs, need
increase vm->tlb_seq, then amdgpu_vm_flush will flush TLB before command
submission.

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