drm/amd/display: enabling stream after HPD low to high happened

[Why]
1. No real HPD plug in/out but HPD happens,
 the driver notifies OS connection changed.
2. No display in target.

When HPD goes low to high,
the driver should regard as HPD and enter setmode flow.

[How]
In this case, even stream didn't change but still retrain.

Signed-off-by: Chiawen Huang <chiawen.huang@amd.com>
Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>