drm/amd/display: Set max VTotal cap for dcn401

[WHY&HOW]
Set max VTotal cap for dcn401 because VTotal
register is only 16 bits wide on dcn401.

Reviewed-by: Chris Park <chris.park@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>