Add initialisation of p_dec->fmt_out so it can be used inside transcode to determine the decoders output format.

Revert change of: VLC_FOURCC('Y','U','V','P') into p_region->fmt.i_chrom on line 449 and fixed some identation for readibility.

- in Add() made osd transcoding selection part of else if
- copy region picture width/height to new region
- added some more debugging
- some cleanup

However not all bugs are gone. Need to figure out where they are.

Decode Teletext subtitles into fourcc 'RGBA', then convert the chroma to fourcc 'YUVA' using video blending and encode YUVA into YUVP and SPU. To be sent to the muxer. However the last step fails. The data never arrives in the muxer.

The transcode_spu_process() only works OK when used with overlay to burn the subtitle in the video. This needs a complete rewrite in the direction of 'osdmenu' subtitles.

  p_spu->p_blend->fmt_in.video.i_chroma = p_region->fmt.i_chroma;