[Why]
Hostvm should be enabled/disabled accordding to
the status of riommu_active, but hostvm always
be disabled on DCN31 which causes underflow

[How]
Set correct hostvm flag on DCN31
Reviewed-by: NCharlene Liu <Charlene.Liu@amd.com>
Acked-by: NWayne Lin <wayne.lin@amd.com>
Signed-off-by: NSherry Wang <Yao.Wang1@amd.com>
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>