encoder: h264: add initial support for H.264 Stereo High profile.

encoder: h264: add initial support for H.264 Stereo High profile.

Add initial support for Subset SPS, Prefix NAL and Slice Extension NAL
for non-base-view streams encoding, and the usual SPS, PPS and Slice
NALs for base-view encoding.

The H.264 Stereo High profile encoding mode will be turned on when the
"num-views" parameter is set to 2. The source (raw) YUV frames will be
considered as Left/Right view, alternatively.

Each of the two views has its own frames reordering pool and reference
frames list management system. Inter-view references are not supported
yet, so the views are encoded independently from each other.

Signed-off-by: Li Xiaowei <xiaowei.a.li@intel.com>
[limited to Stereo High profile per the definition of MAX_NUM_VIEWS]
Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>