Derived the recipe from openembedded.
For poky, we use the ffmpeg lib contained in the package, while
openembedded use the system ffmpeg library.
Removed the PATH_prepend since the latest version of gst-ffmpeg
install program will be called with "-s" unless expilcitly with
"make install-strip".
Update recipe metadata.
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>