kfd_flush_tlb_after_unmap should return true for GFX v9.4.3, to do TLB
heavyweight flush after unmapping from GPU to guarantee that the GPU
will not access pages after they have been unmapped. This also helps
improve the mapping to GPU performance.

Without this, KFD accidently flush TLB after mapping to GPU because the
vm update sequence number is increased by previous unmapping.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>