sceJpeg(): code cleanup and some additions

Few things done here

1. Add ERROR_JPEG_INVALID_VALUE
2. For sceJpegDecodeMJpegYCbCrSuccessively() , it do it as same way as sceJpegDecodeMJpegYCbCr() but with smaller block size
3. Centralize actual codes into sperate __functions to be called by other sce functions