lavc/tiff: Enable decoding of LinearRaw images

"LinearRaw" is a value that the PhotometricInterpretation tag can be set
to on DNG images that contain color information for all channels instead
of being bayer-encoded ("CFA" value).

The DNG decoder is complete enough that we can enable this now.

Sample:
- http://www.rawsamples.ch/raws/nikon/SCANNER_NIKON_LS5000.DNGSigned-off-by: Nick Renieris <velocityra@gmail.com>

libavcodec/tiff.c

@@ -1496,6 +1496,7 @@ static int tiff_decode_tag(TiffContext *s, AVFrame *frame)
         case TIFF_PHOTOMETRIC_SEPARATED:
         case TIFF_PHOTOMETRIC_YCBCR:
         case TIFF_PHOTOMETRIC_CFA:
+        case TIFF_PHOTOMETRIC_LINEAR_RAW: // Used by DNG images
             s->photometric = value;
             break;
         case TIFF_PHOTOMETRIC_ALPHA_MASK:
@@ -1504,7 +1505,6 @@ static int tiff_decode_tag(TiffContext *s, AVFrame *frame)
         case TIFF_PHOTOMETRIC_ITU_LAB:
         case TIFF_PHOTOMETRIC_LOG_L:
         case TIFF_PHOTOMETRIC_LOG_LUV:
-        case TIFF_PHOTOMETRIC_LINEAR_RAW:
             avpriv_report_missing_feature(s->avctx,
                                           "PhotometricInterpretation 0x%04X",
                                           value);