drm/amd/display: Enable HostVM based on rIOMMU active

[Why]
There is underflow and flickering occuring. The
underflow stops when hostvm is forced to active.
According to policy, hostvm should be enabled if riommu
is active, but this is not taken into account when
deciding whether to enable hostvm.

[What]
For DCN314, set hostvm to true if riommu is active.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Gabe Teeger <gabe.teeger@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>