Merge JPEG decoding API from staging branch.

Merge JPEG decoding API from staging branch.

This API is only suitable to Baseline profile.

Cherry-pick'ed from:
336a563: add initial JPEG decoding API
8a7f92b: cosmetics (vertical align)
9092ecf: fix IQ matrix and Huffman table buffer name
5d30647: add "Baseline" suffix the existing data structures
6eefff7: document decoding API is only suitable to baseline profile
de2df79: include <va/va_dec_jpeg.h> into core VA header
979f0e1: drop JPEG-2000 fields from structures for baseline profile
8a6b12d: drop sample_precision since P=8 for baseline profile

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>