drm/amd/display: Display lost signal on playing video

[Why]
When Source extend the vblank to reach the minimum panel
refresh rate, the vtotal length could have 1 line longer
than the maximum supported vtotal.
The reason is we optimized the vtotal/refresh-rate calculation
to get more accurate vtotal number by rounding the calculation
result. But when the target refresh rate is the minimum
refresh rate, the vtotal result could be round up and over
the maximum supported vtotal.

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Signed-off-by: po-tchen <robin.chen@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>