[package] ffmpeg: expose additionnal configuration options (#7837, #8831)

[package] ffmpeg: expose additionnal configuration options (#7837, #8831)

This series, along with previous applied patches, should close tickets #7837 and #8831.

This patch exposes additional decoders and demuxers for FFmpeg in menuconfig, along with other minor changes.

Additional decoders:
flac (Free Lossless Audio Codec)

Additional demuxers:
aac
avi
flac
matroska
mov (mov/mp4/m4a/3gp/3g2/mj2)

zlib is required on matroska/mov to handle compressed headers.

Minor changes:
mp3 demuxer to require the mpegaudio parser. Doesn't do much without it. Matches current ffmpeg behavior.

--target-os=linux as a compile flag. This will be required when cross-compiling in the 0.6 branch, and does no harm here.

Signed-off-by: Ian Leonard <antonlacon_at_gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@26449 3c298f89-4303-0410-b956-a3cf2f4a3e73