ffmpeg: make svn buildable, fix configure options for 0.4.9-pre1, unify, clean up

ffmpeg: make svn buildable, fix configure options for 0.4.9-pre1, unify, clean up
* fix svn using SRCDATE
* reformat EXTRA_OECONF to make the order of the options follow  ./configure --help
* NOTE: --cpu(0.4.9-pre1) equals --arch(svn); while --tune(0.4.9-pre1) equals --cpu(svn)
* NOTE: oe uses --march and --mtune, so the above optimization by ffmpeg (--mcpu) is not really needed
* NOTE: but we try to make --cpu(0.4.9-pre1) or --arch(svn) as close to $TARGET_ARCH as possible
* checked --march and --mtune and $TARGET_CFLAGS are used correctly
* remove unnecessary FLAGS, configure options, oe_runconf(), etc in either svn or pre1
* unify svn and 0.4.9-pre1, however not much can be done for packaging and staging
* QA: add LEAD_SONAME, fix DESCRIPTION, HOME, AUTHOR