d3d12: d3d12_video_encoder_negotiate_current_h264_slices_configuration to use correct mode when intra-refresh is on
When intra-refresh is enabled, per D3D12 encode spec, the slice mode has to be D3D12_VIDEO_ENCODER_FRAME_SUBREGION_LAYOUT_MODE_UNIFORM_PARTITIONING_SUBREGIONS_PER_FRAME.
Validate this in d3d12_video_encoder_negotiate_current_h264_slices_configuration
to use correct mode when intra-refresh is on