ffmpeg: bump to version 1.2.4

Compile tested the following packages which depend on ffmpeg:

freerdp
mpd
gstreamer

For minidlna please see the separate patch for version bump to 1.1.1

Some compile options were taken from OpenELEC:
https://github.com/OpenELEC/OpenELEC.tv/blob/master/packages/multimedia/ffmpeg/build



[Peter: fix ARM VFP option, target tune, enable PIC for !static]
Signed-off-by: Bernd Kuhls <berndkuhls@hotmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>