multimedia/x264: enable FFMS, LAVF, SWSCALE by default

Without FFmpeg-based demuxers x264 CLI can only read raw formats as
source. So, enable more options to allow the binary package not only
write but also read mp4/mkv.

PR: 220694
Approved by: koobs (maintainer)
MFH: 2017Q3 (usability improvement)
Differential Revision: https://reviews.freebsd.org/D11566