[configure] use pkg-config for rtmp detection. fixes linking with newer librtmp versions
[configure] fix static linking when ffmpeg found nettle/hogweed
Merge pull request #4642 from wsnipex/linking-fix

Linking fix [fixes #15139]
[depends] move ffmpeg to unified deps
[configure] remove internal ffmpeg
remove ffmpeg from tree
ffmpeg: remove dll wrappers
add ffmpeg lock manager
todo: refactor to own file
ffmpeg: move callbacks into separate file
remove ffmpeg dlls from generated headers
not removing win32 as this might still be needed?
[rpi] setup-sdk.sh: allow overriding of buildroot and xbmc install paths
also don't require root if not needed
add ffmpeg makefile for rpi
[WIN32] download and compile ffmpeg from remote source.
[WIN32] make XBMC compile, build and run with the ffmpeg link libraries.
[WIN32] use ffmpeg version from tools\depends\target\ffmpeg\FFMPEG-VERSION
[WIN32] prepare mingw build files for jenkins.
[WIN32] removed old mingw build files.
ffmpeg: bump version to 2.2
[depends] add --with-platform=raspberry-pi switch
ffmpeg: change depreciated functions avcodev_alloc/free_frame