drm/amd/display: Set max for prefetch lines on dcn32

[WHY?]
Max number of lines that can be used for prefetch due to type constraints is
63.75.

[HOW?]
Enforce maximum prefetch lines as 63.75.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>