drm/amdkfd: Fix TLB flushing in KFD SVM with no HWS

With no HWS, TLB flushing will not work in SVM code.
Fix this by calling kfd_flush_tlb() which works for both
HWS and no HWS case.

Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>